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 $106.63   11.766%   $119.1761   $119.18   $119.20   $119.20  
  Purchase #2 $63.99   3.397%   $66.1637   $66.16   $66.15   $66.20  
  Purchase #3 $60.89   10.151%   $67.0709   $67.07   $67.05   $67.10  
  Purchase #4 $129.65   6.168%   $137.6468   $137.65   $137.65   $137.60  
  Purchase #5 $220.46   13.613%   $250.4712   $250.47   $250.45   $250.50  
  Purchase #6 $115.94   8.251%   $125.5062   $125.51   $125.50   $125.50  
  Purchase #7 $170.85   6.534%   $182.0133   $182.01   $182.00   $182.00  
  7 purchase totals = $868.41       $948.0482   $948.05   $948.00   $948.10