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 $234.53   11.496%   $261.4916   $261.49   $261.50   $261.50  
  Purchase #2 $144.85   6.782%   $154.6737   $154.67   $154.65   $154.70  
  Purchase #3 $62.91   4.609%   $65.8095   $65.81   $65.80   $65.80  
  Purchase #4 $157.37   7.307%   $168.869   $168.87   $168.85   $168.90  
  Purchase #5 $55.47   12.242%   $62.2606   $62.26   $62.25   $62.30  
  Purchase #6 $185.97   3.701%   $192.8527   $192.85   $192.85   $192.90  
  Purchase #7 $134.35   5.181%   $141.3107   $141.31   $141.30   $141.30  
  7 purchase totals = $975.45       $1,047.2678   $1,047.26   $1,047.20   $1,047.40