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 $30.97   6.459%   $32.9704   $32.97   $32.95   $33.00  
  Purchase #2 $190.75   7.473%   $205.0047   $205.00   $205.00   $205.00  
  Purchase #3 $240.43   8.313%   $260.4169   $260.42   $260.40   $260.40  
  Purchase #4 $94.62   3.698%   $98.119   $98.12   $98.10   $98.10  
  Purchase #5 $192.54   12.738%   $217.0657   $217.07   $217.05   $217.10  
  Purchase #6 $33.40   12.422%   $37.5489   $37.55   $37.55   $37.50  
  Purchase #7 $195.55   7.546%   $210.3062   $210.31   $210.30   $210.30  
  7 purchase totals = $978.26       $1,061.4318   $1,061.44   $1,061.35   $1,061.40