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	$25.35	12.233%	$28.4511	$28.45	$28.45	$28.50
Purchase #2	$242.51	10.600%	$268.2161	$268.22	$268.20	$268.20
Purchase #3	$244.60	5.722%	$258.596	$258.60	$258.60	$258.60
Purchase #4	$87.49	4.573%	$91.4909	$91.49	$91.50	$91.50
Purchase #5	$89.25	6.787%	$95.3074	$95.31	$95.30	$95.30
Purchase #6	$60.87	8.174%	$65.8455	$65.85	$65.85	$65.80
Purchase #7	$135.35	11.215%	$150.5295	$150.53	$150.55	$150.50
7 purchase totals =	$885.42		$958.4365	$958.45	$958.45	$958.40