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	$100.94	7.176%	$108.1835	$108.18	$108.20	$108.20
Purchase #2	$85.97	5.390%	$90.6038	$90.60	$90.60	$90.60
Purchase #3	$246.75	10.438%	$272.5058	$272.51	$272.50	$272.50
Purchase #4	$178.98	7.435%	$192.2872	$192.29	$192.30	$192.30
Purchase #5	$220.87	12.557%	$248.6046	$248.60	$248.60	$248.60
Purchase #6	$156.94	8.852%	$170.8323	$170.83	$170.85	$170.80
Purchase #7	$157.94	4.399%	$164.8878	$164.89	$164.90	$164.90
7 purchase totals =	$1,148.39		$1,247.9050	$1,247.90	$1,247.95	$1,247.90