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 $42.51   8.571%   $46.1535   $46.15   $46.15   $46.20  
  Purchase #2 $169.67   8.423%   $183.9613   $183.96   $183.95   $184.00  
  Purchase #3 $24.86   12.532%   $27.9755   $27.98   $28.00   $28.00  
  Purchase #4 $189.82   13.526%   $215.4951   $215.50   $215.50   $215.50  
  Purchase #5 $143.47   9.669%   $157.3421   $157.34   $157.35   $157.30  
  Purchase #6 $240.48   4.651%   $251.6647   $251.66   $251.65   $251.70  
  Purchase #7 $13.92   11.787%   $15.5608   $15.56   $15.55   $15.60  
  7 purchase totals = $824.73       $898.1530   $898.15   $898.15   $898.30