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 $194.64   12.326%   $218.6313   $218.63   $218.65   $218.60  
  Purchase #2 $234.49   11.665%   $261.8433   $261.84   $261.85   $261.80  
  Purchase #3 $115.28   12.526%   $129.72   $129.72   $129.70   $129.70  
  Purchase #4 $60.56   9.539%   $66.3368   $66.34   $66.35   $66.30  
  Purchase #5 $139.59   9.326%   $152.6082   $152.61   $152.60   $152.60  
  Purchase #6 $57.89   5.662%   $61.1677   $61.17   $61.15   $61.20  
  Purchase #7 $245.47   5.253%   $258.3645   $258.36   $258.35   $258.40  
  7 purchase totals = $1,047.92       $1,148.6718   $1,148.67   $1,148.65   $1,148.60