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 $61.85   8.642%   $67.1951   $67.20   $67.20   $67.20  
  Purchase #2 $210.62   13.780%   $239.6434   $239.64   $239.65   $239.60  
  Purchase #3 $228.81   12.271%   $256.8873   $256.89   $256.90   $256.90  
  Purchase #4 $226.92   13.201%   $256.8757   $256.88   $256.90   $256.90  
  Purchase #5 $152.67   4.726%   $159.8852   $159.89   $159.90   $159.90  
  Purchase #6 $50.36   3.619%   $52.1825   $52.18   $52.20   $52.20  
  Purchase #7 $146.41   10.802%   $162.2252   $162.23   $162.25   $162.20  
  7 purchase totals = $1,077.64       $1,194.8944   $1,194.91   $1,195.00   $1,194.90