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	$129.65	12.849%	$146.3087	$146.31	$146.30	$146.30
Purchase #2	$110.45	5.809%	$116.866	$116.87	$116.85	$116.90
Purchase #3	$202.96	7.111%	$217.3925	$217.39	$217.40	$217.40
Purchase #4	$35.80	11.302%	$39.8461	$39.85	$39.85	$39.80
Purchase #5	$158.51	6.359%	$168.5897	$168.59	$168.60	$168.60
Purchase #6	$34.42	13.727%	$39.1448	$39.14	$39.15	$39.10
Purchase #7	$127.75	7.446%	$137.2623	$137.26	$137.25	$137.30
7 purchase totals =	$799.54		$865.4101	$865.41	$865.40	$865.40