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	$35.68	4.579%	$37.3138	$37.31	$37.30	$37.30
Purchase #2	$55.67	5.162%	$58.5437	$58.54	$58.55	$58.50
Purchase #3	$222.92	9.664%	$244.463	$244.46	$244.45	$244.50
Purchase #4	$29.78	10.692%	$32.9641	$32.96	$32.95	$33.00
Purchase #5	$193.30	10.766%	$214.1107	$214.11	$214.10	$214.10
Purchase #6	$98.63	13.379%	$111.8257	$111.83	$111.85	$111.80
Purchase #7	$76.72	6.382%	$81.6163	$81.62	$81.60	$81.60
7 purchase totals =	$712.70		$780.8373	$780.83	$780.80	$780.80