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 $178.71   13.655%   $203.1129   $203.11   $203.10   $203.10  
  Purchase #2 $225.72   12.659%   $254.2939   $254.29   $254.30   $254.30  
  Purchase #3 $17.60   10.283%   $19.4098   $19.41   $19.40   $19.40  
  Purchase #4 $204.43   5.455%   $215.5817   $215.58   $215.60   $215.60  
  Purchase #5 $143.36   5.595%   $151.381   $151.38   $151.40   $151.40  
  Purchase #6 $48.95   8.142%   $52.9355   $52.94   $52.95   $52.90  
  Purchase #7 $25.86   12.139%   $28.9991   $29.00   $29.00   $29.00  
  7 purchase totals = $844.63       $925.7139   $925.71   $925.75   $925.70