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	$22.47	7.151%	$24.0768	$24.08	$24.10	$24.10
Purchase #2	$97.69	9.416%	$106.8885	$106.89	$106.90	$106.90
Purchase #3	$113.66	12.320%	$127.6629	$127.66	$127.65	$127.70
Purchase #4	$164.73	6.256%	$175.0355	$175.04	$175.05	$175.00
Purchase #5	$11.66	5.476%	$12.2985	$12.30	$12.30	$12.30
Purchase #6	$177.81	12.111%	$199.3446	$199.34	$199.35	$199.30
Purchase #7	$226.56	12.613%	$255.136	$255.14	$255.15	$255.10
7 purchase totals =	$814.58		$900.4428	$900.45	$900.50	$900.40