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 $232.57   9.564%   $254.813   $254.81   $254.80   $254.80  
  Purchase #2 $235.32   13.871%   $267.9612   $267.96   $267.95   $268.00  
  Purchase #3 $40.96   13.458%   $46.4724   $46.47   $46.45   $46.50  
  Purchase #4 $212.26   10.785%   $235.1522   $235.15   $235.15   $235.20  
  Purchase #5 $210.98   13.134%   $238.6901   $238.69   $238.70   $238.70  
  Purchase #6 $42.87   12.371%   $48.1734   $48.17   $48.15   $48.20  
  Purchase #7 $230.85   5.821%   $244.2878   $244.29   $244.30   $244.30  
  7 purchase totals = $1,205.81       $1,335.5501   $1,335.54   $1,335.50   $1,335.70