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	$163.36	5.606%	$172.518	$172.52	$172.50	$172.50
Purchase #2	$137.51	6.373%	$146.2735	$146.27	$146.25	$146.30
Purchase #3	$16.70	12.197%	$18.7369	$18.74	$18.75	$18.70
Purchase #4	$124.59	5.633%	$131.6082	$131.61	$131.60	$131.60
Purchase #5	$136.50	12.671%	$153.7959	$153.80	$153.80	$153.80
Purchase #6	$97.50	11.390%	$108.6053	$108.61	$108.60	$108.60
Purchase #7	$64.44	5.583%	$68.0377	$68.04	$68.05	$68.00
7 purchase totals =	$740.60		$799.5755	$799.59	$799.55	$799.50