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 $217.87   9.376%   $238.2975   $238.30   $238.30   $238.30  
  Purchase #2 $170.38   3.685%   $176.6585   $176.66   $176.65   $176.70  
  Purchase #3 $168.55   3.150%   $173.8593   $173.86   $173.85   $173.90  
  Purchase #4 $86.94   11.838%   $97.232   $97.23   $97.25   $97.20  
  Purchase #5 $155.37   4.677%   $162.6367   $162.64   $162.65   $162.60  
  Purchase #6 $224.92   9.245%   $245.7139   $245.71   $245.70   $245.70  
  Purchase #7 $103.27   8.323%   $111.8652   $111.87   $111.85   $111.90  
  7 purchase totals = $1,127.30       $1,206.2631   $1,206.27   $1,206.25   $1,206.30