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	$86.91	4.604%	$90.9113	$90.91	$90.90	$90.90
Purchase #2	$171.53	13.406%	$194.5253	$194.53	$194.55	$194.50
Purchase #3	$161.80	7.383%	$173.7457	$173.75	$173.75	$173.70
Purchase #4	$80.56	4.467%	$84.1586	$84.16	$84.15	$84.20
Purchase #5	$192.56	11.590%	$214.8777	$214.88	$214.90	$214.90
Purchase #6	$51.66	5.342%	$54.4197	$54.42	$54.40	$54.40
Purchase #7	$91.37	10.135%	$100.6303	$100.63	$100.65	$100.60
7 purchase totals =	$836.39		$913.2686	$913.28	$913.30	$913.20