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	$155.83	12.577%	$175.4287	$175.43	$175.45	$175.40
Purchase #2	$17.89	11.670%	$19.9778	$19.98	$20.00	$20.00
Purchase #3	$127.57	9.615%	$139.8359	$139.84	$139.85	$139.80
Purchase #4	$230.61	7.185%	$247.1793	$247.18	$247.20	$247.20
Purchase #5	$64.74	10.148%	$71.3098	$71.31	$71.30	$71.30
Purchase #6	$182.53	4.844%	$191.3718	$191.37	$191.35	$191.40
Purchase #7	$204.64	13.130%	$231.5092	$231.51	$231.50	$231.50
7 purchase totals =	$983.81		$1,076.6125	$1,076.62	$1,076.65	$1,076.60