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	$236.29	8.141%	$255.5264	$255.53	$255.55	$255.50
Purchase #2	$84.37	11.747%	$94.2809	$94.28	$94.30	$94.30
Purchase #3	$113.39	10.251%	$125.0136	$125.01	$125.00	$125.00
Purchase #4	$149.59	8.741%	$162.6657	$162.67	$162.65	$162.70
Purchase #5	$147.75	11.194%	$164.2891	$164.29	$164.30	$164.30
Purchase #6	$63.47	13.178%	$71.8341	$71.83	$71.85	$71.80
Purchase #7	$60.31	11.213%	$67.0726	$67.07	$67.05	$67.10
7 purchase totals =	$855.17		$940.6824	$940.68	$940.70	$940.70