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	$246.48	3.306%	$254.6286	$254.63	$254.65	$254.60
Purchase #2	$229.82	9.422%	$251.4736	$251.47	$251.45	$251.50
Purchase #3	$129.50	6.485%	$137.8981	$137.90	$137.90	$137.90
Purchase #4	$12.31	10.561%	$13.6101	$13.61	$13.60	$13.60
Purchase #5	$248.31	12.175%	$278.5417	$278.54	$278.55	$278.50
Purchase #6	$160.49	7.538%	$172.5877	$172.59	$172.60	$172.60
Purchase #7	$120.88	7.649%	$130.1261	$130.13	$130.15	$130.10
7 purchase totals =	$1,147.79		$1,238.8659	$1,238.87	$1,238.90	$1,238.80