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 $88.35   11.467%   $98.4811   $98.48   $98.50   $98.50  
  Purchase #2 $218.65   5.787%   $231.3033   $231.30   $231.30   $231.30  
  Purchase #3 $149.29   6.344%   $158.761   $158.76   $158.75   $158.80  
  Purchase #4 $46.76   6.324%   $49.7171   $49.72   $49.70   $49.70  
  Purchase #5 $105.73   9.735%   $116.0228   $116.02   $116.00   $116.00  
  Purchase #6 $165.27   5.239%   $173.9285   $173.93   $173.95   $173.90  
  Purchase #7 $26.88   9.329%   $29.3876   $29.39   $29.40   $29.40  
  7 purchase totals = $800.93       $857.6014   $857.60   $857.60   $857.60