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 $66.80   10.640%   $73.9075   $73.91   $73.90   $73.90  
  Purchase #2 $186.30   9.477%   $203.9557   $203.96   $203.95   $204.00  
  Purchase #3 $47.99   4.482%   $50.1409   $50.14   $50.15   $50.10  
  Purchase #4 $29.53   5.695%   $31.2117   $31.21   $31.20   $31.20  
  Purchase #5 $248.42   5.338%   $261.6807   $261.68   $261.70   $261.70  
  Purchase #6 $23.76   6.497%   $25.3037   $25.30   $25.30   $25.30  
  Purchase #7 $25.43   3.215%   $26.2476   $26.25   $26.25   $26.20  
  7 purchase totals = $628.23       $672.4478   $672.45   $672.45   $672.40