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 $43.39   11.777%   $48.5   $48.50   $48.50   $48.50  
  Purchase #2 $122.99   13.543%   $139.6465   $139.65   $139.65   $139.60  
  Purchase #3 $78.84   5.304%   $83.0217   $83.02   $83.00   $83.00  
  Purchase #4 $224.50   9.290%   $245.3561   $245.36   $245.35   $245.40  
  Purchase #5 $119.26   4.501%   $124.6279   $124.63   $124.65   $124.60  
  Purchase #6 $215.27   11.870%   $240.8225   $240.82   $240.80   $240.80  
  Purchase #7 $137.46   3.703%   $142.5501   $142.55   $142.55   $142.60  
  7 purchase totals = $941.71       $1,024.5248   $1,024.53   $1,024.50   $1,024.50