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 $60.31   9.438%   $66.0021   $66.00   $66.00   $66.00  
  Purchase #2 $210.74   7.553%   $226.6572   $226.66   $226.65   $226.70  
  Purchase #3 $41.88   12.168%   $46.976   $46.98   $47.00   $47.00  
  Purchase #4 $213.86   3.721%   $221.8177   $221.82   $221.80   $221.80  
  Purchase #5 $146.30   11.758%   $163.502   $163.50   $163.50   $163.50  
  Purchase #6 $58.34   5.796%   $61.7214   $61.72   $61.70   $61.70  
  Purchase #7 $124.88   13.519%   $141.7625   $141.76   $141.75   $141.80  
  7 purchase totals = $856.31       $928.4389   $928.44   $928.40   $928.50