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 $220.61   12.329%   $247.809   $247.81   $247.80   $247.80  
  Purchase #2 $184.68   5.374%   $194.6047   $194.60   $194.60   $194.60  
  Purchase #3 $35.56   13.781%   $40.4605   $40.46   $40.45   $40.50  
  Purchase #4 $151.72   4.738%   $158.9085   $158.91   $158.90   $158.90  
  Purchase #5 $66.29   6.544%   $70.628   $70.63   $70.65   $70.60  
  Purchase #6 $233.76   3.577%   $242.1216   $242.12   $242.10   $242.10  
  Purchase #7 $8.46   11.837%   $9.4614   $9.46   $9.45   $9.50  
  7 purchase totals = $901.08       $963.9937   $963.99   $963.95   $964.00