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	$188.91	4.133%	$196.7177	$196.72	$196.70	$196.70
Purchase #2	$68.87	9.649%	$75.5153	$75.52	$75.50	$75.50
Purchase #3	$88.81	6.266%	$94.3748	$94.37	$94.35	$94.40
Purchase #4	$35.78	13.609%	$40.6493	$40.65	$40.65	$40.60
Purchase #5	$143.95	12.862%	$162.4648	$162.46	$162.45	$162.50
Purchase #6	$107.32	3.548%	$111.1277	$111.13	$111.15	$111.10
Purchase #7	$145.70	9.194%	$159.0957	$159.10	$159.10	$159.10
7 purchase totals =	$779.34		$839.9453	$839.95	$839.90	$839.90