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	$143.69	6.632%	$153.2195	$153.22	$153.20	$153.20
Purchase #2	$59.46	7.814%	$64.1062	$64.11	$64.10	$64.10
Purchase #3	$126.91	13.707%	$144.3056	$144.31	$144.30	$144.30
Purchase #4	$228.50	10.212%	$251.8344	$251.83	$251.85	$251.80
Purchase #5	$155.95	9.237%	$170.3551	$170.36	$170.35	$170.40
Purchase #6	$123.73	5.798%	$130.9039	$130.90	$130.90	$130.90
Purchase #7	$121.85	4.794%	$127.6915	$127.69	$127.70	$127.70
7 purchase totals =	$960.09		$1,042.4162	$1,042.42	$1,042.40	$1,042.40