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 $117.78   6.620%   $125.577   $125.58   $125.60   $125.60  
  Purchase #2 $58.51   10.452%   $64.6255   $64.63   $64.65   $64.60  
  Purchase #3 $32.88   10.378%   $36.2923   $36.29   $36.30   $36.30  
  Purchase #4 $222.63   5.307%   $234.445   $234.45   $234.45   $234.40  
  Purchase #5 $79.44   6.749%   $84.8014   $84.80   $84.80   $84.80  
  Purchase #6 $62.76   9.387%   $68.6513   $68.65   $68.65   $68.70  
  Purchase #7 $154.82   8.480%   $167.9487   $167.95   $167.95   $167.90  
  7 purchase totals = $728.82       $782.3412   $782.35   $782.40   $782.30