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	$80.80	5.686%	$85.3943	$85.39	$85.40	$85.40
Purchase #2	$157.89	10.122%	$173.8716	$173.87	$173.85	$173.90
Purchase #3	$81.51	3.661%	$84.4941	$84.49	$84.50	$84.50
Purchase #4	$99.56	4.420%	$103.9606	$103.96	$103.95	$104.00
Purchase #5	$73.68	8.463%	$79.9155	$79.92	$79.90	$79.90
Purchase #6	$137.87	9.739%	$151.2972	$151.30	$151.30	$151.30
Purchase #7	$109.59	12.680%	$123.486	$123.49	$123.50	$123.50
7 purchase totals =	$740.90		$802.4193	$802.42	$802.40	$802.50