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	$73.26	10.301%	$80.8065	$80.81	$80.80	$80.80
Purchase #2	$134.68	4.514%	$140.7595	$140.76	$140.75	$140.80
Purchase #3	$146.87	3.819%	$152.479	$152.48	$152.50	$152.50
Purchase #4	$214.67	5.491%	$226.4575	$226.46	$226.45	$226.50
Purchase #5	$156.52	10.551%	$173.0344	$173.03	$173.05	$173.00
Purchase #6	$133.60	6.126%	$141.7843	$141.78	$141.80	$141.80
Purchase #7	$119.54	6.366%	$127.1499	$127.15	$127.15	$127.10
7 purchase totals =	$979.14		$1,042.4711	$1,042.47	$1,042.50	$1,042.50