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	$178.68	8.234%	$193.3925	$193.39	$193.40	$193.40
Purchase #2	$138.66	6.561%	$147.7575	$147.76	$147.75	$147.80
Purchase #3	$198.96	11.779%	$222.3955	$222.40	$222.40	$222.40
Purchase #4	$24.92	13.342%	$28.2448	$28.24	$28.25	$28.20
Purchase #5	$19.97	12.733%	$22.5128	$22.51	$22.50	$22.50
Purchase #6	$98.65	13.281%	$111.7517	$111.75	$111.75	$111.80
Purchase #7	$64.89	11.853%	$72.5814	$72.58	$72.60	$72.60
7 purchase totals =	$724.73		$798.6362	$798.63	$798.65	$798.70