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 $104.95   13.668%   $119.2946   $119.29   $119.30   $119.30  
  Purchase #2 $53.40   8.104%   $57.7275   $57.73   $57.75   $57.70  
  Purchase #3 $154.42   9.314%   $168.8027   $168.80   $168.80   $168.80  
  Purchase #4 $46.46   6.391%   $49.4293   $49.43   $49.45   $49.40  
  Purchase #5 $67.41   8.713%   $73.2834   $73.28   $73.30   $73.30  
  Purchase #6 $199.92   3.804%   $207.525   $207.53   $207.55   $207.50  
  Purchase #7 $87.61   12.103%   $98.2134   $98.21   $98.20   $98.20  
  7 purchase totals = $714.17       $774.2759   $774.27   $774.35   $774.20