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 $29.49   8.661%   $32.0441   $32.04   $32.05   $32.00  
  Purchase #2 $203.85   4.262%   $212.5381   $212.54   $212.55   $212.50  
  Purchase #3 $97.62   13.512%   $110.8104   $110.81   $110.80   $110.80  
  Purchase #4 $125.59   13.420%   $142.4442   $142.44   $142.45   $142.40  
  Purchase #5 $219.51   11.271%   $244.251   $244.25   $244.25   $244.30  
  Purchase #6 $149.36   3.793%   $155.0252   $155.03   $155.05   $155.00  
  Purchase #7 $32.25   11.290%   $35.891   $35.89   $35.90   $35.90  
  7 purchase totals = $857.67       $933.0040   $933.00   $933.05   $932.90