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 $48.74   12.283%   $54.7267   $54.73   $54.75   $54.70  
  Purchase #2 $223.96   6.343%   $238.1658   $238.17   $238.15   $238.20  
  Purchase #3 $59.73   9.752%   $65.5549   $65.55   $65.55   $65.60  
  Purchase #4 $90.68   11.528%   $101.1336   $101.13   $101.15   $101.10  
  Purchase #5 $55.86   5.455%   $58.9072   $58.91   $58.90   $58.90  
  Purchase #6 $32.85   4.486%   $34.3237   $34.32   $34.30   $34.30  
  Purchase #7 $232.79   3.193%   $240.223   $240.22   $240.20   $240.20  
  7 purchase totals = $744.61       $793.0349   $793.03   $793.00   $793.00