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	$44.85	12.166%	$50.3065	$50.31	$50.30	$50.30
Purchase #2	$104.56	9.153%	$114.1304	$114.13	$114.15	$114.10
Purchase #3	$231.67	13.250%	$262.3663	$262.37	$262.35	$262.40
Purchase #4	$134.72	6.372%	$143.3044	$143.30	$143.30	$143.30
Purchase #5	$123.45	6.531%	$131.5125	$131.51	$131.50	$131.50
Purchase #6	$133.68	9.408%	$146.2566	$146.26	$146.25	$146.30
Purchase #7	$134.29	12.103%	$150.5431	$150.54	$150.55	$150.50
7 purchase totals =	$907.22		$998.4198	$998.42	$998.40	$998.40