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 $92.27   4.726%   $96.6307   $96.63   $96.65   $96.60  
  Purchase #2 $169.32   11.181%   $188.2517   $188.25   $188.25   $188.30  
  Purchase #3 $70.93   5.121%   $74.5623   $74.56   $74.55   $74.60  
  Purchase #4 $26.49   5.739%   $28.0103   $28.01   $28.00   $28.00  
  Purchase #5 $58.44   3.825%   $60.6753   $60.68   $60.70   $60.70  
  Purchase #6 $158.85   10.145%   $174.9653   $174.97   $174.95   $175.00  
  Purchase #7 $191.40   3.414%   $197.9344   $197.93   $197.95   $197.90  
  7 purchase totals = $767.70       $821.0300   $821.03   $821.05   $821.10