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 $215.53   8.263%   $233.3392   $233.34   $233.35   $233.30  
  Purchase #2 $116.42   4.265%   $121.3853   $121.39   $121.40   $121.40  
  Purchase #3 $241.25   12.219%   $270.7283   $270.73   $270.75   $270.70  
  Purchase #4 $112.94   3.387%   $116.7653   $116.77   $116.75   $116.80  
  Purchase #5 $217.74   5.847%   $230.4713   $230.47   $230.45   $230.50  
  Purchase #6 $94.69   6.357%   $100.7094   $100.71   $100.70   $100.70  
  Purchase #7 $113.98   5.682%   $120.4563   $120.46   $120.45   $120.50  
  7 purchase totals = $1,112.55       $1,193.8551   $1,193.87   $1,193.85   $1,193.90