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	$38.38	5.733%	$40.5803	$40.58	$40.60	$40.60
Purchase #2	$83.81	13.692%	$95.2853	$95.29	$95.30	$95.30
Purchase #3	$60.72	12.326%	$68.2043	$68.20	$68.20	$68.20
Purchase #4	$133.51	8.629%	$145.0306	$145.03	$145.05	$145.00
Purchase #5	$40.96	11.766%	$45.7794	$45.78	$45.80	$45.80
Purchase #6	$162.27	12.185%	$182.0426	$182.04	$182.05	$182.00
Purchase #7	$41.39	7.325%	$44.4218	$44.42	$44.40	$44.40
7 purchase totals =	$561.04		$621.3443	$621.34	$621.40	$621.30