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	$123.28	8.223%	$133.4173	$133.42	$133.40	$133.40
Purchase #2	$95.64	4.125%	$99.5852	$99.59	$99.60	$99.60
Purchase #3	$115.92	10.314%	$127.876	$127.88	$127.90	$127.90
Purchase #4	$146.78	7.668%	$158.0351	$158.04	$158.05	$158.00
Purchase #5	$224.62	5.820%	$237.6929	$237.69	$237.70	$237.70
Purchase #6	$141.45	7.851%	$152.5552	$152.56	$152.55	$152.60
Purchase #7	$127.74	11.338%	$142.2232	$142.22	$142.20	$142.20
7 purchase totals =	$975.43		$1,051.3849	$1,051.40	$1,051.40	$1,051.40