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	$162.37	6.861%	$173.5102	$173.51	$173.50	$173.50
Purchase #2	$50.81	5.358%	$53.5324	$53.53	$53.55	$53.50
Purchase #3	$78.48	12.153%	$88.0177	$88.02	$88.00	$88.00
Purchase #4	$9.83	3.225%	$10.147	$10.15	$10.15	$10.10
Purchase #5	$111.52	12.498%	$125.4578	$125.46	$125.45	$125.50
Purchase #6	$145.45	4.762%	$152.3763	$152.38	$152.40	$152.40
Purchase #7	$34.55	7.235%	$37.0497	$37.05	$37.05	$37.00
7 purchase totals =	$593.01		$640.0911	$640.10	$640.10	$640.00