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	$17.82	13.686%	$20.2588	$20.26	$20.25	$20.30
Purchase #2	$87.54	3.819%	$90.8832	$90.88	$90.90	$90.90
Purchase #3	$78.83	12.403%	$88.6073	$88.61	$88.60	$88.60
Purchase #4	$126.31	7.861%	$136.2392	$136.24	$136.25	$136.20
Purchase #5	$156.37	5.671%	$165.2377	$165.24	$165.25	$165.20
Purchase #6	$49.41	4.351%	$51.5598	$51.56	$51.55	$51.60
Purchase #7	$15.72	8.309%	$17.0262	$17.03	$17.05	$17.00
7 purchase totals =	$532.00		$569.8122	$569.82	$569.85	$569.80