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	$6.76	7.636%	$7.2762	$7.28	$7.30	$7.30
Purchase #2	$145.44	6.604%	$155.0449	$155.04	$155.05	$155.00
Purchase #3	$76.36	6.789%	$81.5441	$81.54	$81.55	$81.50
Purchase #4	$81.55	11.525%	$90.9486	$90.95	$90.95	$90.90
Purchase #5	$73.66	9.757%	$80.847	$80.85	$80.85	$80.80
Purchase #6	$11.26	10.733%	$12.4685	$12.47	$12.45	$12.50
Purchase #7	$168.78	13.853%	$192.1611	$192.16	$192.15	$192.20
7 purchase totals =	$563.81		$620.2904	$620.29	$620.30	$620.20