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	$45.40	7.757%	$48.9217	$48.92	$48.90	$48.90
Purchase #2	$244.90	13.657%	$278.346	$278.35	$278.35	$278.30
Purchase #3	$29.77	9.147%	$32.4931	$32.49	$32.50	$32.50
Purchase #4	$172.54	8.139%	$186.583	$186.58	$186.60	$186.60
Purchase #5	$137.47	10.131%	$151.3971	$151.40	$151.40	$151.40
Purchase #6	$37.60	12.579%	$42.3297	$42.33	$42.35	$42.30
Purchase #7	$38.36	11.265%	$42.6813	$42.68	$42.70	$42.70
7 purchase totals =	$706.04		$782.7519	$782.75	$782.80	$782.70