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	$39.91	8.144%	$43.1603	$43.16	$43.15	$43.20
Purchase #2	$164.61	6.679%	$175.6043	$175.60	$175.60	$175.60
Purchase #3	$204.87	9.159%	$223.634	$223.63	$223.65	$223.60
Purchase #4	$61.83	6.359%	$65.7618	$65.76	$65.75	$65.80
Purchase #5	$37.49	7.841%	$40.4296	$40.43	$40.45	$40.40
Purchase #6	$197.63	5.445%	$208.391	$208.39	$208.40	$208.40
Purchase #7	$60.98	3.204%	$62.9338	$62.93	$62.95	$62.90
7 purchase totals =	$767.32		$819.9148	$819.90	$819.95	$819.90