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	$19.63	4.439%	$20.5014	$20.50	$20.50	$20.50
Purchase #2	$214.43	12.324%	$240.8564	$240.86	$240.85	$240.90
Purchase #3	$238.77	11.520%	$266.2763	$266.28	$266.30	$266.30
Purchase #4	$49.62	9.418%	$54.2932	$54.29	$54.30	$54.30
Purchase #5	$84.60	5.486%	$89.2412	$89.24	$89.25	$89.20
Purchase #6	$82.45	12.192%	$92.5023	$92.50	$92.50	$92.50
Purchase #7	$30.25	9.762%	$33.203	$33.20	$33.20	$33.20
7 purchase totals =	$719.75		$796.8738	$796.87	$796.90	$796.90