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 $61.31   7.593%   $65.9653   $65.97   $65.95   $66.00  
  Purchase #2 $195.51   13.570%   $222.0407   $222.04   $222.05   $222.00  
  Purchase #3 $162.29   11.231%   $180.5168   $180.52   $180.50   $180.50  
  Purchase #4 $110.75   11.544%   $123.535   $123.54   $123.55   $123.50  
  Purchase #5 $146.91   8.326%   $159.1417   $159.14   $159.15   $159.10  
  Purchase #6 $49.26   9.561%   $53.9697   $53.97   $53.95   $54.00  
  Purchase #7 $115.39   8.627%   $125.3447   $125.34   $125.35   $125.30  
  7 purchase totals = $841.42       $930.5139   $930.52   $930.50   $930.40