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	$227.30	6.343%	$241.7176	$241.72	$241.70	$241.70
Purchase #2	$31.49	11.420%	$35.0862	$35.09	$35.10	$35.10
Purchase #3	$49.66	8.552%	$53.9069	$53.91	$53.90	$53.90
Purchase #4	$156.89	3.867%	$162.9569	$162.96	$162.95	$163.00
Purchase #5	$127.34	3.383%	$131.6479	$131.65	$131.65	$131.60
Purchase #6	$90.43	10.664%	$100.0735	$100.07	$100.05	$100.10
Purchase #7	$127.54	11.347%	$142.012	$142.01	$142.00	$142.00
7 purchase totals =	$810.65		$867.4010	$867.41	$867.35	$867.40