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	$19.34	3.677%	$20.0511	$20.05	$20.05	$20.10
Purchase #2	$182.32	5.468%	$192.2893	$192.29	$192.30	$192.30
Purchase #3	$93.70	6.236%	$99.5431	$99.54	$99.55	$99.50
Purchase #4	$11.43	12.723%	$12.8842	$12.88	$12.90	$12.90
Purchase #5	$241.72	5.833%	$255.8195	$255.82	$255.80	$255.80
Purchase #6	$131.52	11.569%	$146.7355	$146.74	$146.75	$146.70
Purchase #7	$108.50	10.529%	$119.924	$119.92	$119.90	$119.90
7 purchase totals =	$788.53		$847.2467	$847.24	$847.25	$847.20