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	$165.90	6.438%	$176.5806	$176.58	$176.60	$176.60
Purchase #2	$39.92	4.339%	$41.6521	$41.65	$41.65	$41.70
Purchase #3	$59.81	10.830%	$66.2874	$66.29	$66.30	$66.30
Purchase #4	$62.47	12.762%	$70.4424	$70.44	$70.45	$70.40
Purchase #5	$118.32	7.496%	$127.1893	$127.19	$127.20	$127.20
Purchase #6	$175.33	9.686%	$192.3125	$192.31	$192.30	$192.30
Purchase #7	$224.79	13.639%	$255.4491	$255.45	$255.45	$255.40
7 purchase totals =	$846.54		$929.9134	$929.91	$929.95	$929.90