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	$86.69	3.166%	$89.4346	$89.43	$89.45	$89.40
Purchase #2	$22.80	13.830%	$25.9532	$25.95	$25.95	$26.00
Purchase #3	$177.67	11.748%	$198.5427	$198.54	$198.55	$198.50
Purchase #4	$214.31	8.775%	$233.1157	$233.12	$233.10	$233.10
Purchase #5	$160.42	8.176%	$173.5359	$173.54	$173.55	$173.50
Purchase #6	$60.39	4.758%	$63.2634	$63.26	$63.25	$63.30
Purchase #7	$56.88	5.170%	$59.8207	$59.82	$59.80	$59.80
7 purchase totals =	$779.16		$843.6662	$843.66	$843.65	$843.60