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	$225.67	13.282%	$255.6435	$255.64	$255.65	$255.60
Purchase #2	$72.83	8.310%	$78.8822	$78.88	$78.90	$78.90
Purchase #3	$21.92	3.837%	$22.7611	$22.76	$22.75	$22.80
Purchase #4	$34.49	5.635%	$36.4335	$36.43	$36.45	$36.40
Purchase #5	$96.87	8.430%	$105.0361	$105.04	$105.05	$105.00
Purchase #6	$129.58	3.627%	$134.2799	$134.28	$134.30	$134.30
Purchase #7	$176.96	6.105%	$187.7634	$187.76	$187.75	$187.80
7 purchase totals =	$758.32		$820.7997	$820.79	$820.85	$820.80