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 $84.61   10.544%   $93.5313   $93.53   $93.55   $93.50  
  Purchase #2 $50.84   3.329%   $52.5325   $52.53   $52.55   $52.50  
  Purchase #3 $250.65   10.365%   $276.6299   $276.63   $276.65   $276.60  
  Purchase #4 $9.46   4.181%   $9.8555   $9.86   $9.85   $9.90  
  Purchase #5 $32.34   7.809%   $34.8654   $34.87   $34.85   $34.90  
  Purchase #6 $51.30   10.345%   $56.607   $56.61   $56.60   $56.60  
  Purchase #7 $202.98   3.191%   $209.4571   $209.46   $209.45   $209.50  
  7 purchase totals = $682.18       $733.4787   $733.49   $733.50   $733.50