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	$54.55	12.104%	$61.1527	$61.15	$61.15	$61.20
Purchase #2	$82.67	10.823%	$91.6174	$91.62	$91.60	$91.60
Purchase #3	$171.67	4.728%	$179.7866	$179.79	$179.80	$179.80
Purchase #4	$99.73	11.818%	$111.5161	$111.52	$111.50	$111.50
Purchase #5	$97.32	6.555%	$103.6993	$103.70	$103.70	$103.70
Purchase #6	$186.63	10.181%	$205.6308	$205.63	$205.65	$205.60
Purchase #7	$214.65	11.866%	$240.1204	$240.12	$240.10	$240.10
7 purchase totals =	$907.22		$993.5233	$993.53	$993.50	$993.50