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 $44.62   9.269%   $48.7558   $48.76   $48.75   $48.80  
  Purchase #2 $55.96   7.201%   $59.9897   $59.99   $60.00   $60.00  
  Purchase #3 $139.43   13.867%   $158.7648   $158.76   $158.75   $158.80  
  Purchase #4 $43.86   13.457%   $49.7622   $49.76   $49.75   $49.80  
  Purchase #5 $231.40   13.497%   $262.6321   $262.63   $262.65   $262.60  
  Purchase #6 $104.94   12.774%   $118.345   $118.35   $118.35   $118.30  
  Purchase #7 $217.98   12.209%   $244.5932   $244.59   $244.60   $244.60  
  7 purchase totals = $838.19       $942.8428   $942.84   $942.85   $942.90