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 $106.95   11.552%   $119.3049   $119.30   $119.30   $119.30  
  Purchase #2 $21.88   10.648%   $24.2098   $24.21   $24.20   $24.20  
  Purchase #3 $61.54   12.154%   $69.0196   $69.02   $69.00   $69.00  
  Purchase #4 $168.48   13.530%   $191.2753   $191.28   $191.30   $191.30  
  Purchase #5 $218.64   8.730%   $237.7273   $237.73   $237.75   $237.70  
  Purchase #6 $138.57   13.684%   $157.5319   $157.53   $157.55   $157.50  
  Purchase #7 $234.28   11.431%   $261.0605   $261.06   $261.05   $261.10  
  7 purchase totals = $950.34       $1,060.1293   $1,060.13   $1,060.15   $1,060.10