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 $58.47   13.599%   $66.4213   $66.42   $66.40   $66.40  
  Purchase #2 $105.51   10.749%   $116.8513   $116.85   $116.85   $116.90  
  Purchase #3 $116.40   7.773%   $125.4478   $125.45   $125.45   $125.40  
  Purchase #4 $25.41   3.852%   $26.3888   $26.39   $26.40   $26.40  
  Purchase #5 $110.39   9.841%   $121.2535   $121.25   $121.25   $121.30  
  Purchase #6 $244.25   12.190%   $274.0241   $274.02   $274.00   $274.00  
  Purchase #7 $208.60   8.135%   $225.5696   $225.57   $225.55   $225.60  
  7 purchase totals = $869.03       $955.9564   $955.95   $955.90   $956.00