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 $244.67   6.639%   $260.9136   $260.91   $260.90   $260.90  
  Purchase #2 $195.31   3.807%   $202.7455   $202.75   $202.75   $202.70  
  Purchase #3 $250.66   7.503%   $269.467   $269.47   $269.45   $269.50  
  Purchase #4 $132.98   6.829%   $142.0612   $142.06   $142.05   $142.10  
  Purchase #5 $200.26   5.105%   $210.4833   $210.48   $210.50   $210.50  
  Purchase #6 $146.64   3.566%   $151.8692   $151.87   $151.85   $151.90  
  Purchase #7 $102.70   10.172%   $113.1466   $113.15   $113.15   $113.10  
  7 purchase totals = $1,273.22       $1,350.6864   $1,350.69   $1,350.65   $1,350.70