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 $32.53   4.340%   $33.9418   $33.94   $33.95   $33.90  
  Purchase #2 $170.72   11.460%   $190.2845   $190.28   $190.30   $190.30  
  Purchase #3 $65.52   3.811%   $68.017   $68.02   $68.00   $68.00  
  Purchase #4 $198.94   9.415%   $217.6702   $217.67   $217.65   $217.70  
  Purchase #5 $29.28   13.728%   $33.2996   $33.30   $33.30   $33.30  
  Purchase #6 $201.30   7.289%   $215.9728   $215.97   $215.95   $216.00  
  Purchase #7 $60.86   5.388%   $64.1391   $64.14   $64.15   $64.10  
  7 purchase totals = $759.15       $823.3250   $823.32   $823.30   $823.30