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	$24.63	6.729%	$26.2874	$26.29	$26.30	$26.30
Purchase #2	$110.32	5.407%	$116.285	$116.29	$116.30	$116.30
Purchase #3	$228.57	11.671%	$255.2464	$255.25	$255.25	$255.20
Purchase #4	$95.68	10.335%	$105.5685	$105.57	$105.55	$105.60
Purchase #5	$118.62	7.733%	$127.7929	$127.79	$127.80	$127.80
Purchase #6	$100.65	5.577%	$106.2633	$106.26	$106.25	$106.30
Purchase #7	$55.38	13.155%	$62.6652	$62.67	$62.65	$62.70
7 purchase totals =	$733.85		$800.1087	$800.12	$800.10	$800.20