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	$141.28	3.702%	$146.5102	$146.51	$146.50	$146.50
Purchase #2	$53.68	10.790%	$59.4721	$59.47	$59.45	$59.50
Purchase #3	$66.68	12.569%	$75.061	$75.06	$75.05	$75.10
Purchase #4	$31.50	13.736%	$35.8268	$35.83	$35.85	$35.80
Purchase #5	$107.32	9.558%	$117.5776	$117.58	$117.60	$117.60
Purchase #6	$32.29	11.420%	$35.9775	$35.98	$36.00	$36.00
Purchase #7	$106.79	11.586%	$119.1627	$119.16	$119.15	$119.20
7 purchase totals =	$539.54		$589.5879	$589.59	$589.60	$589.70