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 $129.58   3.797%   $134.5002   $134.50   $134.50   $134.50  
  Purchase #2 $126.64   8.121%   $136.9244   $136.92   $136.90   $136.90  
  Purchase #3 $71.77   8.162%   $77.6279   $77.63   $77.65   $77.60  
  Purchase #4 $42.87   11.136%   $47.644   $47.64   $47.65   $47.60  
  Purchase #5 $48.91   4.859%   $51.2865   $51.29   $51.30   $51.30  
  Purchase #6 $77.82   9.151%   $84.9413   $84.94   $84.95   $84.90  
  Purchase #7 $245.54   6.715%   $262.028   $262.03   $262.05   $262.00  
  7 purchase totals = $743.13       $794.9523   $794.95   $795.00   $794.80