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	$38.90	4.389%	$40.6073	$40.61	$40.60	$40.60
Purchase #2	$118.51	11.704%	$132.3804	$132.38	$132.40	$132.40
Purchase #3	$235.87	4.796%	$247.1823	$247.18	$247.20	$247.20
Purchase #4	$55.73	6.382%	$59.2867	$59.29	$59.30	$59.30
Purchase #5	$64.42	10.839%	$71.4025	$71.40	$71.40	$71.40
Purchase #6	$122.61	4.369%	$127.9668	$127.97	$127.95	$128.00
Purchase #7	$11.95	8.717%	$12.9917	$12.99	$13.00	$13.00
7 purchase totals =	$647.99		$691.8177	$691.82	$691.85	$691.90