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 $209.90   8.263%   $227.244   $227.24   $227.25   $227.20  
  Purchase #2 $65.71   9.221%   $71.7691   $71.77   $71.75   $71.80  
  Purchase #3 $29.38   3.132%   $30.3002   $30.30   $30.30   $30.30  
  Purchase #4 $99.41   13.527%   $112.8572   $112.86   $112.85   $112.90  
  Purchase #5 $62.72   13.506%   $71.191   $71.19   $71.20   $71.20  
  Purchase #6 $24.89   8.150%   $26.9185   $26.92   $26.90   $26.90  
  Purchase #7 $155.72   8.291%   $168.6307   $168.63   $168.65   $168.60  
  7 purchase totals = $647.73       $708.9107   $708.91   $708.90   $708.90