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 $105.41   13.365%   $119.498   $119.50   $119.50   $119.50  
  Purchase #2 $233.85   11.791%   $261.4233   $261.42   $261.40   $261.40  
  Purchase #3 $150.66   5.668%   $159.1994   $159.20   $159.20   $159.20  
  Purchase #4 $63.28   7.112%   $67.7805   $67.78   $67.80   $67.80  
  Purchase #5 $206.81   4.628%   $216.3812   $216.38   $216.40   $216.40  
  Purchase #6 $234.47   10.220%   $258.4328   $258.43   $258.45   $258.40  
  Purchase #7 $220.93   13.843%   $251.5133   $251.51   $251.50   $251.50  
  7 purchase totals = $1,215.41       $1,334.2285   $1,334.22   $1,334.25   $1,334.20