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 $61.42   8.352%   $66.5498   $66.55   $66.55   $66.50  
  Purchase #2 $109.45   9.534%   $119.885   $119.89   $119.90   $119.90  
  Purchase #3 $103.82   9.366%   $113.5438   $113.54   $113.55   $113.50  
  Purchase #4 $245.74   6.406%   $261.4821   $261.48   $261.50   $261.50  
  Purchase #5 $117.35   5.833%   $124.195   $124.20   $124.20   $124.20  
  Purchase #6 $24.33   3.867%   $25.2708   $25.27   $25.25   $25.30  
  Purchase #7 $90.45   9.251%   $98.8175   $98.82   $98.80   $98.80  
  7 purchase totals = $752.56       $809.7440   $809.75   $809.75   $809.70