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	$165.41	12.522%	$186.1226	$186.12	$186.10	$186.10
Purchase #2	$30.27	6.707%	$32.3002	$32.30	$32.30	$32.30
Purchase #3	$42.73	9.630%	$46.8449	$46.84	$46.85	$46.80
Purchase #4	$240.50	13.448%	$272.8424	$272.84	$272.85	$272.80
Purchase #5	$231.65	3.874%	$240.6241	$240.62	$240.60	$240.60
Purchase #6	$123.66	10.380%	$136.4959	$136.50	$136.50	$136.50
Purchase #7	$158.38	4.451%	$165.4295	$165.43	$165.45	$165.40
7 purchase totals =	$992.60		$1,080.6596	$1,080.65	$1,080.65	$1,080.50