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	$18.47	5.758%	$19.5335	$19.53	$19.55	$19.50
Purchase #2	$101.50	9.851%	$111.4988	$111.50	$111.50	$111.50
Purchase #3	$96.41	8.354%	$104.4641	$104.46	$104.45	$104.50
Purchase #4	$125.69	13.751%	$142.9736	$142.97	$142.95	$143.00
Purchase #5	$53.26	13.480%	$60.4394	$60.44	$60.45	$60.40
Purchase #6	$167.40	13.585%	$190.1413	$190.14	$190.15	$190.10
Purchase #7	$129.58	12.114%	$145.2773	$145.28	$145.30	$145.30
7 purchase totals =	$692.31		$774.3280	$774.32	$774.35	$774.30