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	$35.76	6.642%	$38.1352	$38.14	$38.15	$38.10
Purchase #2	$246.92	3.208%	$254.8412	$254.84	$254.85	$254.80
Purchase #3	$9.58	7.626%	$10.3106	$10.31	$10.30	$10.30
Purchase #4	$31.91	11.538%	$35.5918	$35.59	$35.60	$35.60
Purchase #5	$204.59	8.246%	$221.4605	$221.46	$221.45	$221.50
Purchase #6	$91.92	8.820%	$100.0273	$100.03	$100.05	$100.00
Purchase #7	$137.92	4.562%	$144.2119	$144.21	$144.20	$144.20
7 purchase totals =	$758.60		$804.5785	$804.58	$804.60	$804.50