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	$22.54	10.468%	$24.8995	$24.90	$24.90	$24.90
Purchase #2	$28.92	12.867%	$32.6411	$32.64	$32.65	$32.60
Purchase #3	$46.82	6.519%	$49.8722	$49.87	$49.85	$49.90
Purchase #4	$27.72	4.163%	$28.874	$28.87	$28.85	$28.90
Purchase #5	$241.34	3.111%	$248.8481	$248.85	$248.85	$248.80
Purchase #6	$32.27	5.508%	$34.0474	$34.05	$34.05	$34.00
Purchase #7	$85.74	6.286%	$91.1296	$91.13	$91.15	$91.10
7 purchase totals =	$485.35		$510.3119	$510.31	$510.30	$510.20