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	$127.91	7.580%	$137.6056	$137.61	$137.60	$137.60
Purchase #2	$59.39	11.107%	$65.9864	$65.99	$66.00	$66.00
Purchase #3	$41.98	11.214%	$46.6876	$46.69	$46.70	$46.70
Purchase #4	$59.94	9.434%	$65.5947	$65.59	$65.60	$65.60
Purchase #5	$243.49	13.404%	$276.1274	$276.13	$276.15	$276.10
Purchase #6	$47.92	6.508%	$51.0386	$51.04	$51.05	$51.00
Purchase #7	$33.55	10.237%	$36.9845	$36.98	$37.00	$37.00
7 purchase totals =	$614.18		$680.0248	$680.03	$680.10	$680.00