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	$153.32	13.114%	$173.4264	$173.43	$173.45	$173.40
Purchase #2	$61.95	9.459%	$67.8099	$67.81	$67.80	$67.80
Purchase #3	$172.78	8.792%	$187.9708	$187.97	$187.95	$188.00
Purchase #4	$161.57	9.438%	$176.819	$176.82	$176.80	$176.80
Purchase #5	$82.29	8.160%	$89.0049	$89.00	$89.00	$89.00
Purchase #6	$112.77	13.344%	$127.818	$127.82	$127.80	$127.80
Purchase #7	$12.62	9.193%	$13.7802	$13.78	$13.80	$13.80
7 purchase totals =	$757.30		$836.6292	$836.63	$836.60	$836.60