Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.29   8.869%   $126.6038   $126.60   $126.60   $126.60  
  Purchase #2 $198.39   7.316%   $212.9042   $212.90   $212.90   $212.90  
  Purchase #3 $162.43   3.660%   $168.3749   $168.37   $168.35   $168.40  
  Purchase #4 $116.25   13.624%   $132.0879   $132.09   $132.10   $132.10  
  Purchase #5 $131.83   5.144%   $138.6113   $138.61   $138.60   $138.60  
  Purchase #6 $237.62   13.624%   $269.9933   $269.99   $270.00   $270.00  
  Purchase #7 $152.64   11.834%   $170.7034   $170.70   $170.70   $170.70  
  7 purchase totals = $1,115.45       $1,219.2788   $1,219.26   $1,219.25   $1,219.30