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	$102.31	7.795%	$110.2851	$110.29	$110.30	$110.30
Purchase #2	$173.91	5.821%	$184.0333	$184.03	$184.05	$184.00
Purchase #3	$222.50	3.584%	$230.4744	$230.47	$230.45	$230.50
Purchase #4	$139.27	13.802%	$158.492	$158.49	$158.50	$158.50
Purchase #5	$185.30	13.606%	$210.5119	$210.51	$210.50	$210.50
Purchase #6	$37.92	5.174%	$39.882	$39.88	$39.90	$39.90
Purchase #7	$38.53	5.213%	$40.5386	$40.54	$40.55	$40.50
7 purchase totals =	$899.74		$974.2173	$974.21	$974.25	$974.20