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 $33.25   9.536%   $36.4207   $36.42   $36.40   $36.40  
  Purchase #2 $244.47   8.382%   $264.9615   $264.96   $264.95   $265.00  
  Purchase #3 $122.59   8.175%   $132.6117   $132.61   $132.60   $132.60  
  Purchase #4 $184.64   11.213%   $205.3437   $205.34   $205.35   $205.30  
  Purchase #5 $48.82   4.704%   $51.1165   $51.12   $51.10   $51.10  
  Purchase #6 $105.35   13.321%   $119.3837   $119.38   $119.40   $119.40  
  Purchase #7 $92.43   10.739%   $102.3561   $102.36   $102.35   $102.40  
  7 purchase totals = $831.55       $912.1939   $912.19   $912.15   $912.20