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	$250.73	8.236%	$271.3801	$271.38	$271.40	$271.40
Purchase #2	$70.59	3.267%	$72.8962	$72.90	$72.90	$72.90
Purchase #3	$175.72	4.816%	$184.1827	$184.18	$184.20	$184.20
Purchase #4	$120.68	5.462%	$127.2715	$127.27	$127.25	$127.30
Purchase #5	$160.27	11.733%	$179.0745	$179.07	$179.05	$179.10
Purchase #6	$247.37	3.337%	$255.6247	$255.62	$255.60	$255.60
Purchase #7	$182.32	12.557%	$205.2139	$205.21	$205.20	$205.20
7 purchase totals =	$1,207.68		$1,295.6436	$1,295.63	$1,295.60	$1,295.70