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	$82.60	7.613%	$88.8883	$88.89	$88.90	$88.90
Purchase #2	$144.51	6.153%	$153.4017	$153.40	$153.40	$153.40
Purchase #3	$132.61	12.244%	$148.8468	$148.85	$148.85	$148.80
Purchase #4	$101.26	9.718%	$111.1004	$111.10	$111.10	$111.10
Purchase #5	$40.38	4.500%	$42.1971	$42.20	$42.20	$42.20
Purchase #6	$100.71	5.544%	$106.2934	$106.29	$106.30	$106.30
Purchase #7	$130.36	9.349%	$142.5474	$142.55	$142.55	$142.50
7 purchase totals =	$732.43		$793.2751	$793.28	$793.30	$793.20