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 $118.68   6.389%   $126.2625   $126.26   $126.25   $126.30  
  Purchase #2 $58.43   4.848%   $61.2627   $61.26   $61.25   $61.30  
  Purchase #3 $53.84   9.399%   $58.9004   $58.90   $58.90   $58.90  
  Purchase #4 $13.76   12.579%   $15.4909   $15.49   $15.50   $15.50  
  Purchase #5 $55.32   13.400%   $62.7329   $62.73   $62.75   $62.70  
  Purchase #6 $114.90   5.837%   $121.6067   $121.61   $121.60   $121.60  
  Purchase #7 $217.80   13.784%   $247.8216   $247.82   $247.80   $247.80  
  7 purchase totals = $632.73       $694.0777   $694.07   $694.05   $694.10