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 $241.35   8.455%   $261.7561   $261.76   $261.75   $261.80  
  Purchase #2 $232.92   7.437%   $250.2423   $250.24   $250.25   $250.20  
  Purchase #3 $174.65   12.157%   $195.8822   $195.88   $195.90   $195.90  
  Purchase #4 $242.76   6.215%   $257.8475   $257.85   $257.85   $257.80  
  Purchase #5 $53.53   12.770%   $60.3658   $60.37   $60.35   $60.40  
  Purchase #6 $82.66   13.762%   $94.0357   $94.04   $94.05   $94.00  
  Purchase #7 $103.66   4.314%   $108.1319   $108.13   $108.15   $108.10  
  7 purchase totals = $1,131.53       $1,228.2615   $1,228.27   $1,228.30   $1,228.20