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	$174.72	3.368%	$180.6046	$180.60	$180.60	$180.60
Purchase #2	$216.29	10.445%	$238.8815	$238.88	$238.90	$238.90
Purchase #3	$233.45	13.821%	$265.7151	$265.72	$265.70	$265.70
Purchase #4	$55.64	11.719%	$62.1605	$62.16	$62.15	$62.20
Purchase #5	$130.84	4.443%	$136.6532	$136.65	$136.65	$136.70
Purchase #6	$244.88	3.757%	$254.0801	$254.08	$254.10	$254.10
Purchase #7	$158.45	8.696%	$172.2288	$172.23	$172.25	$172.20
7 purchase totals =	$1,214.27		$1,310.3238	$1,310.32	$1,310.35	$1,310.40