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	$74.56	5.742%	$78.8412	$78.84	$78.85	$78.80
Purchase #2	$45.60	6.403%	$48.5198	$48.52	$48.50	$48.50
Purchase #3	$108.76	13.495%	$123.4372	$123.44	$123.45	$123.40
Purchase #4	$187.59	9.162%	$204.777	$204.78	$204.80	$204.80
Purchase #5	$152.96	7.707%	$164.7486	$164.75	$164.75	$164.70
Purchase #6	$161.91	6.413%	$172.2933	$172.29	$172.30	$172.30
Purchase #7	$51.97	12.428%	$58.4288	$58.43	$58.45	$58.40
7 purchase totals =	$783.35		$851.0459	$851.05	$851.10	$850.90