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 $241.27   8.486%   $261.7442   $261.74   $261.75   $261.70  
  Purchase #2 $17.88   6.332%   $19.0122   $19.01   $19.00   $19.00  
  Purchase #3 $115.85   9.342%   $126.6727   $126.67   $126.65   $126.70  
  Purchase #4 $69.91   4.793%   $73.2608   $73.26   $73.25   $73.30  
  Purchase #5 $47.71   7.848%   $51.4543   $51.45   $51.45   $51.50  
  Purchase #6 $71.30   8.175%   $77.1288   $77.13   $77.15   $77.10  
  Purchase #7 $209.93   5.674%   $221.8414   $221.84   $221.85   $221.80  
  7 purchase totals = $773.85       $831.1144   $831.10   $831.10   $831.10