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 $210.98   11.516%   $235.2765   $235.28   $235.30   $235.30  
  Purchase #2 $109.91   5.445%   $115.8946   $115.89   $115.90   $115.90  
  Purchase #3 $167.82   9.264%   $183.3668   $183.37   $183.35   $183.40  
  Purchase #4 $233.49   11.748%   $260.9204   $260.92   $260.90   $260.90  
  Purchase #5 $174.38   6.149%   $185.1026   $185.10   $185.10   $185.10  
  Purchase #6 $168.27   3.484%   $174.1325   $174.13   $174.15   $174.10  
  Purchase #7 $180.75   7.725%   $194.7129   $194.71   $194.70   $194.70  
  7 purchase totals = $1,245.60       $1,349.4063   $1,349.40   $1,349.40   $1,349.40