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	$24.68	3.364%	$25.5102	$25.51	$25.50	$25.50
Purchase #2	$86.51	3.323%	$89.3847	$89.38	$89.40	$89.40
Purchase #3	$18.60	12.392%	$20.9049	$20.90	$20.90	$20.90
Purchase #4	$20.88	6.717%	$22.2825	$22.28	$22.30	$22.30
Purchase #5	$76.93	8.479%	$83.4529	$83.45	$83.45	$83.50
Purchase #6	$132.52	9.501%	$145.1107	$145.11	$145.10	$145.10
Purchase #7	$160.29	7.509%	$172.3262	$172.33	$172.35	$172.30
7 purchase totals =	$520.41		$558.9721	$558.96	$559.00	$559.00