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	$109.52	3.314%	$113.1495	$113.15	$113.15	$113.10
Purchase #2	$24.95	13.801%	$28.3933	$28.39	$28.40	$28.40
Purchase #3	$112.28	13.761%	$127.7309	$127.73	$127.75	$127.70
Purchase #4	$68.29	5.832%	$72.2727	$72.27	$72.25	$72.30
Purchase #5	$71.70	4.266%	$74.7587	$74.76	$74.75	$74.80
Purchase #6	$44.33	11.834%	$49.576	$49.58	$49.60	$49.60
Purchase #7	$214.83	12.862%	$242.4614	$242.46	$242.45	$242.50
7 purchase totals =	$645.90		$708.3425	$708.34	$708.35	$708.40