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	$71.87	11.588%	$80.1983	$80.20	$80.20	$80.20
Purchase #2	$193.29	12.282%	$217.0299	$217.03	$217.05	$217.00
Purchase #3	$74.47	10.866%	$82.5619	$82.56	$82.55	$82.60
Purchase #4	$82.41	12.733%	$92.9033	$92.90	$92.90	$92.90
Purchase #5	$135.36	3.274%	$139.7917	$139.79	$139.80	$139.80
Purchase #6	$114.31	11.584%	$127.5517	$127.55	$127.55	$127.60
Purchase #7	$137.49	12.651%	$154.8839	$154.88	$154.90	$154.90
7 purchase totals =	$809.20		$894.9207	$894.91	$894.95	$895.00