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	$46.28	6.634%	$49.3502	$49.35	$49.35	$49.40
Purchase #2	$141.87	7.741%	$152.8522	$152.85	$152.85	$152.90
Purchase #3	$20.53	8.478%	$22.2705	$22.27	$22.25	$22.30
Purchase #4	$70.57	4.664%	$73.8614	$73.86	$73.85	$73.90
Purchase #5	$146.42	3.500%	$151.5447	$151.54	$151.55	$151.50
Purchase #6	$35.75	8.110%	$38.6493	$38.65	$38.65	$38.60
Purchase #7	$100.92	8.577%	$109.5759	$109.58	$109.60	$109.60
7 purchase totals =	$562.34		$598.1042	$598.10	$598.10	$598.20