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	$205.85	13.811%	$234.2799	$234.28	$234.30	$234.30
Purchase #2	$41.86	8.588%	$45.4549	$45.45	$45.45	$45.50
Purchase #3	$172.67	7.636%	$185.8551	$185.86	$185.85	$185.90
Purchase #4	$203.74	8.484%	$221.0253	$221.03	$221.05	$221.00
Purchase #5	$112.28	9.246%	$122.6614	$122.66	$122.65	$122.70
Purchase #6	$45.40	6.365%	$48.2897	$48.29	$48.30	$48.30
Purchase #7	$77.37	6.821%	$82.6474	$82.65	$82.65	$82.60
7 purchase totals =	$859.17		$940.2137	$940.22	$940.25	$940.30