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 $57.49   7.756%   $61.9489   $61.95   $61.95   $61.90  
  Purchase #2 $146.37   4.802%   $153.3987   $153.40   $153.40   $153.40  
  Purchase #3 $210.89   9.692%   $231.3295   $231.33   $231.35   $231.30  
  Purchase #4 $71.42   3.215%   $73.7162   $73.72   $73.70   $73.70  
  Purchase #5 $104.79   9.621%   $114.8718   $114.87   $114.85   $114.90  
  Purchase #6 $68.87   10.143%   $75.8555   $75.86   $75.85   $75.90  
  Purchase #7 $77.85   6.367%   $82.8067   $82.81   $82.80   $82.80  
  7 purchase totals = $737.68       $793.9273   $793.94   $793.90   $793.90