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 $89.63   10.155%   $98.7319   $98.73   $98.75   $98.70  
  Purchase #2 $50.81   7.183%   $54.4597   $54.46   $54.45   $54.50  
  Purchase #3 $64.43   8.436%   $69.8653   $69.87   $69.85   $69.90  
  Purchase #4 $154.41   12.242%   $173.3129   $173.31   $173.30   $173.30  
  Purchase #5 $214.93   6.384%   $228.6511   $228.65   $228.65   $228.70  
  Purchase #6 $173.36   12.463%   $194.9659   $194.97   $194.95   $195.00  
  Purchase #7 $250.33   4.369%   $261.2669   $261.27   $261.25   $261.30  
  7 purchase totals = $997.90       $1,081.2537   $1,081.26   $1,081.20   $1,081.40