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 $87.84   11.681%   $98.1006   $98.10   $98.10   $98.10  
  Purchase #2 $156.26   3.432%   $161.6228   $161.62   $161.60   $161.60  
  Purchase #3 $18.52   13.105%   $20.947   $20.95   $20.95   $20.90  
  Purchase #4 $121.35   13.412%   $137.6255   $137.63   $137.65   $137.60  
  Purchase #5 $175.96   12.767%   $198.4248   $198.42   $198.40   $198.40  
  Purchase #6 $47.34   12.517%   $53.2655   $53.27   $53.25   $53.30  
  Purchase #7 $96.97   4.328%   $101.1669   $101.17   $101.15   $101.20  
  7 purchase totals = $704.24       $771.1531   $771.16   $771.10   $771.10