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	$100.93	4.750%	$105.7242	$105.72	$105.70	$105.70
Purchase #2	$216.81	4.433%	$226.4212	$226.42	$226.40	$226.40
Purchase #3	$74.95	4.313%	$78.1826	$78.18	$78.20	$78.20
Purchase #4	$81.45	10.380%	$89.9045	$89.90	$89.90	$89.90
Purchase #5	$89.63	13.623%	$101.8403	$101.84	$101.85	$101.80
Purchase #6	$93.56	5.113%	$98.3437	$98.34	$98.35	$98.30
Purchase #7	$136.82	8.733%	$148.7685	$148.77	$148.75	$148.80
7 purchase totals =	$794.15		$849.1850	$849.17	$849.15	$849.10