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 $247.88   11.593%   $276.6167   $276.62   $276.60   $276.60  
  Purchase #2 $232.66   12.210%   $261.0678   $261.07   $261.05   $261.10  
  Purchase #3 $119.41   5.513%   $125.9931   $125.99   $126.00   $126.00  
  Purchase #4 $21.35   12.463%   $24.0109   $24.01   $24.00   $24.00  
  Purchase #5 $112.48   5.439%   $118.5978   $118.60   $118.60   $118.60  
  Purchase #6 $244.77   9.827%   $268.8235   $268.82   $268.80   $268.80  
  Purchase #7 $43.99   4.528%   $45.9819   $45.98   $46.00   $46.00  
  7 purchase totals = $1,022.54       $1,121.0917   $1,121.09   $1,121.05   $1,121.10