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	$32.43	6.442%	$34.5191	$34.52	$34.50	$34.50
Purchase #2	$176.30	7.620%	$189.7341	$189.73	$189.75	$189.70
Purchase #3	$99.70	11.716%	$111.3809	$111.38	$111.40	$111.40
Purchase #4	$80.61	8.255%	$87.2644	$87.26	$87.25	$87.30
Purchase #5	$169.28	11.527%	$188.7929	$188.79	$188.80	$188.80
Purchase #6	$54.44	4.281%	$56.7706	$56.77	$56.75	$56.80
Purchase #7	$132.78	10.683%	$146.9649	$146.96	$146.95	$147.00
7 purchase totals =	$745.54		$815.4269	$815.41	$815.40	$815.50