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	$53.82	6.170%	$57.1407	$57.14	$57.15	$57.10
Purchase #2	$111.60	4.508%	$116.6309	$116.63	$116.65	$116.60
Purchase #3	$131.98	5.422%	$139.136	$139.14	$139.15	$139.10
Purchase #4	$152.49	12.752%	$171.9355	$171.94	$171.95	$171.90
Purchase #5	$25.30	4.799%	$26.5141	$26.51	$26.50	$26.50
Purchase #6	$229.82	9.247%	$251.0715	$251.07	$251.05	$251.10
Purchase #7	$42.46	6.389%	$45.1728	$45.17	$45.15	$45.20
7 purchase totals =	$747.47		$807.6015	$807.60	$807.60	$807.50