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	$36.25	3.663%	$37.5778	$37.58	$37.60	$37.60
Purchase #2	$118.38	13.318%	$134.1458	$134.15	$134.15	$134.10
Purchase #3	$134.69	10.419%	$148.7234	$148.72	$148.70	$148.70
Purchase #4	$180.52	6.499%	$192.252	$192.25	$192.25	$192.30
Purchase #5	$17.43	3.277%	$18.0012	$18.00	$18.00	$18.00
Purchase #6	$72.62	13.126%	$82.1521	$82.15	$82.15	$82.20
Purchase #7	$33.68	4.126%	$35.0696	$35.07	$35.05	$35.10
7 purchase totals =	$593.57		$647.9219	$647.92	$647.90	$648.00