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	$83.72	8.386%	$90.7408	$90.74	$90.75	$90.70
Purchase #2	$234.66	13.551%	$266.4588	$266.46	$266.45	$266.50
Purchase #3	$185.67	3.607%	$192.3671	$192.37	$192.35	$192.40
Purchase #4	$230.51	7.238%	$247.1943	$247.19	$247.20	$247.20
Purchase #5	$174.64	5.581%	$184.3867	$184.39	$184.40	$184.40
Purchase #6	$179.51	10.478%	$198.3191	$198.32	$198.30	$198.30
Purchase #7	$165.72	3.820%	$172.0505	$172.05	$172.05	$172.10
7 purchase totals =	$1,254.43		$1,351.5173	$1,351.52	$1,351.50	$1,351.60