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 $227.27   11.732%   $253.9333   $253.93   $253.95   $253.90  
  Purchase #2 $57.98   11.548%   $64.6755   $64.68   $64.70   $64.70  
  Purchase #3 $88.52   4.527%   $92.5273   $92.53   $92.55   $92.50  
  Purchase #4 $94.32   5.528%   $99.534   $99.53   $99.55   $99.50  
  Purchase #5 $187.31   10.313%   $206.6273   $206.63   $206.65   $206.60  
  Purchase #6 $177.27   10.108%   $195.1885   $195.19   $195.20   $195.20  
  Purchase #7 $56.29   3.564%   $58.2962   $58.30   $58.30   $58.30  
  7 purchase totals = $888.96       $970.7821   $970.79   $970.90   $970.70