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 $119.80   11.567%   $133.6573   $133.66   $133.65   $133.70  
  Purchase #2 $92.57   11.769%   $103.4646   $103.46   $103.45   $103.50  
  Purchase #3 $217.84   8.605%   $236.5851   $236.59   $236.60   $236.60  
  Purchase #4 $141.28   10.549%   $156.1836   $156.18   $156.20   $156.20  
  Purchase #5 $86.46   5.192%   $90.949   $90.95   $90.95   $90.90  
  Purchase #6 $21.45   7.460%   $23.0502   $23.05   $23.05   $23.10  
  Purchase #7 $194.54   9.740%   $213.4882   $213.49   $213.50   $213.50  
  7 purchase totals = $873.94       $957.3780   $957.38   $957.40   $957.50