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 $81.64   13.606%   $92.7479   $92.75   $92.75   $92.70  
  Purchase #2 $162.28   8.525%   $176.1144   $176.11   $176.10   $176.10  
  Purchase #3 $35.27   9.674%   $38.682   $38.68   $38.70   $38.70  
  Purchase #4 $154.41   9.582%   $169.2056   $169.21   $169.20   $169.20  
  Purchase #5 $249.78   4.836%   $261.8594   $261.86   $261.85   $261.90  
  Purchase #6 $176.87   11.263%   $196.7909   $196.79   $196.80   $196.80  
  Purchase #7 $53.81   6.448%   $57.2797   $57.28   $57.30   $57.30  
  7 purchase totals = $914.06       $992.6799   $992.68   $992.70   $992.70