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	$33.70	5.707%	$35.6233	$35.62	$35.60	$35.60
Purchase #2	$46.96	13.668%	$53.3785	$53.38	$53.40	$53.40
Purchase #3	$233.39	4.321%	$243.4748	$243.47	$243.45	$243.50
Purchase #4	$35.48	6.305%	$37.717	$37.72	$37.70	$37.70
Purchase #5	$137.67	10.531%	$152.168	$152.17	$152.15	$152.20
Purchase #6	$209.96	8.671%	$228.1656	$228.17	$228.15	$228.20
Purchase #7	$73.26	7.722%	$78.9171	$78.92	$78.90	$78.90
7 purchase totals =	$770.42		$829.4443	$829.45	$829.35	$829.50