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 $225.89   4.466%   $235.9782   $235.98   $236.00   $236.00  
  Purchase #2 $86.33   12.388%   $97.0246   $97.02   $97.00   $97.00  
  Purchase #3 $200.93   8.708%   $218.427   $218.43   $218.45   $218.40  
  Purchase #4 $29.30   9.802%   $32.172   $32.17   $32.15   $32.20  
  Purchase #5 $83.44   13.314%   $94.5492   $94.55   $94.55   $94.50  
  Purchase #6 $173.75   12.322%   $195.1595   $195.16   $195.15   $195.20  
  Purchase #7 $58.54   3.115%   $60.3635   $60.36   $60.35   $60.40  
  7 purchase totals = $858.18       $933.6740   $933.67   $933.65   $933.70