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 $119.97   13.327%   $135.9584   $135.96   $135.95   $136.00  
  Purchase #2 $61.89   4.545%   $64.7029   $64.70   $64.70   $64.70  
  Purchase #3 $171.43   8.812%   $186.5364   $186.54   $186.55   $186.50  
  Purchase #4 $244.35   8.534%   $265.2028   $265.20   $265.20   $265.20  
  Purchase #5 $199.81   7.774%   $215.3432   $215.34   $215.35   $215.30  
  Purchase #6 $95.51   7.128%   $102.318   $102.32   $102.30   $102.30  
  Purchase #7 $162.41   10.576%   $179.5865   $179.59   $179.60   $179.60  
  7 purchase totals = $1,055.37       $1,149.6482   $1,149.65   $1,149.65   $1,149.60