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	$73.83	9.300%	$80.6962	$80.70	$80.70	$80.70
Purchase #2	$86.51	4.306%	$90.2351	$90.24	$90.25	$90.20
Purchase #3	$128.34	4.624%	$134.2744	$134.27	$134.25	$134.30
Purchase #4	$40.61	13.862%	$46.2394	$46.24	$46.25	$46.20
Purchase #5	$164.62	9.445%	$180.1684	$180.17	$180.15	$180.20
Purchase #6	$141.46	3.735%	$146.7435	$146.74	$146.75	$146.70
Purchase #7	$36.91	10.257%	$40.6959	$40.70	$40.70	$40.70
7 purchase totals =	$672.28		$719.0529	$719.06	$719.05	$719.00