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	$61.34	6.486%	$65.3185	$65.32	$65.30	$65.30
Purchase #2	$121.37	5.204%	$127.6861	$127.69	$127.70	$127.70
Purchase #3	$52.29	11.201%	$58.147	$58.15	$58.15	$58.10
Purchase #4	$141.30	3.231%	$145.8654	$145.87	$145.85	$145.90
Purchase #5	$234.93	5.468%	$247.776	$247.78	$247.80	$247.80
Purchase #6	$128.77	12.261%	$144.5585	$144.56	$144.55	$144.60
Purchase #7	$49.92	5.326%	$52.5787	$52.58	$52.60	$52.60
7 purchase totals =	$789.92		$841.9302	$841.95	$841.95	$842.00