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 $22.97   7.181%   $24.6195   $24.62   $24.60   $24.60  
  Purchase #2 $229.92   5.678%   $242.9749   $242.97   $242.95   $243.00  
  Purchase #3 $95.49   3.683%   $99.0069   $99.01   $99.00   $99.00  
  Purchase #4 $59.99   11.262%   $66.7461   $66.75   $66.75   $66.70  
  Purchase #5 $15.62   13.398%   $17.7128   $17.71   $17.70   $17.70  
  Purchase #6 $221.42   3.423%   $228.9992   $229.00   $229.00   $229.00  
  Purchase #7 $43.84   9.518%   $48.0127   $48.01   $48.00   $48.00  
  7 purchase totals = $689.25       $728.0721   $728.07   $728.00   $728.00