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 $117.43   6.677%   $125.2708   $125.27   $125.25   $125.30  
  Purchase #2 $177.28   8.163%   $191.7514   $191.75   $191.75   $191.80  
  Purchase #3 $169.63   7.397%   $182.1775   $182.18   $182.20   $182.20  
  Purchase #4 $250.30   4.342%   $261.168   $261.17   $261.15   $261.20  
  Purchase #5 $122.59   10.778%   $135.8028   $135.80   $135.80   $135.80  
  Purchase #6 $82.35   4.185%   $85.7963   $85.80   $85.80   $85.80  
  Purchase #7 $20.92   6.723%   $22.3265   $22.33   $22.35   $22.30  
  7 purchase totals = $940.50       $1,004.2933   $1,004.30   $1,004.30   $1,004.40