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 $248.57   4.759%   $260.3994   $260.40   $260.40   $260.40  
  Purchase #2 $124.93   13.824%   $142.2003   $142.20   $142.20   $142.20  
  Purchase #3 $45.44   7.203%   $48.713   $48.71   $48.70   $48.70  
  Purchase #4 $77.62   12.313%   $87.1774   $87.18   $87.20   $87.20  
  Purchase #5 $193.51   4.616%   $202.4424   $202.44   $202.45   $202.40  
  Purchase #6 $162.99   8.528%   $176.8898   $176.89   $176.90   $176.90  
  Purchase #7 $210.67   11.208%   $234.2819   $234.28   $234.30   $234.30  
  7 purchase totals = $1,063.73       $1,152.1042   $1,152.10   $1,152.15   $1,152.10