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	$25.93	9.422%	$28.3731	$28.37	$28.35	$28.40
Purchase #2	$68.34	5.124%	$71.8417	$71.84	$71.85	$71.80
Purchase #3	$221.38	9.684%	$242.8184	$242.82	$242.80	$242.80
Purchase #4	$43.75	3.277%	$45.1837	$45.18	$45.20	$45.20
Purchase #5	$44.91	13.651%	$51.0407	$51.04	$51.05	$51.00
Purchase #6	$244.42	13.573%	$277.5951	$277.60	$277.60	$277.60
Purchase #7	$242.50	7.758%	$261.3132	$261.31	$261.30	$261.30
7 purchase totals =	$891.23		$978.1659	$978.16	$978.15	$978.10