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	$12.79	6.211%	$13.5844	$13.58	$13.60	$13.60
Purchase #2	$149.41	7.804%	$161.07	$161.07	$161.05	$161.10
Purchase #3	$74.53	11.529%	$83.1226	$83.12	$83.10	$83.10
Purchase #4	$139.74	11.329%	$155.5711	$155.57	$155.55	$155.60
Purchase #5	$9.42	12.169%	$10.5663	$10.57	$10.55	$10.60
Purchase #6	$30.65	4.603%	$32.0608	$32.06	$32.05	$32.10
Purchase #7	$40.85	3.136%	$42.1311	$42.13	$42.15	$42.10
7 purchase totals =	$457.39		$498.1063	$498.10	$498.05	$498.20