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	$145.66	13.404%	$165.1843	$165.18	$165.20	$165.20
Purchase #2	$222.79	10.806%	$246.8647	$246.86	$246.85	$246.90
Purchase #3	$9.36	4.256%	$9.7584	$9.76	$9.75	$9.80
Purchase #4	$94.48	11.707%	$105.5408	$105.54	$105.55	$105.50
Purchase #5	$66.85	3.667%	$69.3014	$69.30	$69.30	$69.30
Purchase #6	$85.58	5.176%	$90.0096	$90.01	$90.00	$90.00
Purchase #7	$88.38	13.697%	$100.4854	$100.49	$100.50	$100.50
7 purchase totals =	$713.10		$787.1446	$787.14	$787.15	$787.20