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	$40.50	12.602%	$45.6038	$45.60	$45.60	$45.60
Purchase #2	$45.73	7.322%	$49.0784	$49.08	$49.10	$49.10
Purchase #3	$71.85	6.412%	$76.457	$76.46	$76.45	$76.50
Purchase #4	$217.84	13.563%	$247.3856	$247.39	$247.40	$247.40
Purchase #5	$120.37	10.758%	$133.3194	$133.32	$133.30	$133.30
Purchase #6	$133.47	5.697%	$141.0738	$141.07	$141.05	$141.10
Purchase #7	$92.59	13.670%	$105.2471	$105.25	$105.25	$105.20
7 purchase totals =	$722.35		$798.1651	$798.17	$798.15	$798.20