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	$104.91	6.155%	$111.3672	$111.37	$111.35	$111.40
Purchase #2	$66.55	6.810%	$71.0821	$71.08	$71.10	$71.10
Purchase #3	$242.70	13.235%	$274.8213	$274.82	$274.80	$274.80
Purchase #4	$114.40	11.268%	$127.2906	$127.29	$127.30	$127.30
Purchase #5	$40.44	12.604%	$45.5371	$45.54	$45.55	$45.50
Purchase #6	$154.34	13.415%	$175.0447	$175.04	$175.05	$175.00
Purchase #7	$38.92	9.702%	$42.696	$42.70	$42.70	$42.70
7 purchase totals =	$762.26		$847.8390	$847.84	$847.85	$847.80