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 $73.37   4.598%   $76.7436   $76.74   $76.75   $76.70  
  Purchase #2 $244.30   11.283%   $271.8644   $271.86   $271.85   $271.90  
  Purchase #3 $149.57   9.751%   $164.1546   $164.15   $164.15   $164.20  
  Purchase #4 $69.61   9.496%   $76.2202   $76.22   $76.20   $76.20  
  Purchase #5 $176.83   13.480%   $200.6667   $200.67   $200.65   $200.70  
  Purchase #6 $242.92   13.520%   $275.7628   $275.76   $275.75   $275.80  
  Purchase #7 $160.81   13.387%   $182.3376   $182.34   $182.35   $182.30  
  7 purchase totals = $1,117.41       $1,247.7499   $1,247.74   $1,247.70   $1,247.80