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 $108.96   8.530%   $118.2543   $118.25   $118.25   $118.30  
  Purchase #2 $82.62   11.762%   $92.3378   $92.34   $92.35   $92.30  
  Purchase #3 $56.40   8.644%   $61.2752   $61.28   $61.30   $61.30  
  Purchase #4 $8.92   9.202%   $9.7408   $9.74   $9.75   $9.70  
  Purchase #5 $243.41   7.367%   $261.342   $261.34   $261.35   $261.30  
  Purchase #6 $204.71   3.373%   $211.6149   $211.61   $211.60   $211.60  
  Purchase #7 $144.53   11.219%   $160.7448   $160.74   $160.75   $160.70  
  7 purchase totals = $849.55       $915.3098   $915.30   $915.35   $915.20