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 $64.38   13.857%   $73.3011   $73.30   $73.30   $73.30  
  Purchase #2 $141.95   10.749%   $157.2082   $157.21   $157.20   $157.20  
  Purchase #3 $123.89   12.134%   $138.9228   $138.92   $138.90   $138.90  
  Purchase #4 $19.99   11.852%   $22.3592   $22.36   $22.35   $22.40  
  Purchase #5 $57.62   6.743%   $61.5053   $61.51   $61.50   $61.50  
  Purchase #6 $217.87   12.211%   $244.4741   $244.47   $244.45   $244.50  
  Purchase #7 $243.89   3.868%   $253.3237   $253.32   $253.30   $253.30  
  7 purchase totals = $869.59       $951.0944   $951.09   $951.00   $951.10