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	$135.46	7.174%	$145.1779	$145.18	$145.20	$145.20
Purchase #2	$133.59	12.327%	$150.0576	$150.06	$150.05	$150.10
Purchase #3	$37.89	11.758%	$42.3451	$42.35	$42.35	$42.30
Purchase #4	$139.56	13.527%	$158.4383	$158.44	$158.45	$158.40
Purchase #5	$243.37	13.323%	$275.7942	$275.79	$275.80	$275.80
Purchase #6	$237.78	6.534%	$253.3165	$253.32	$253.30	$253.30
Purchase #7	$234.34	10.578%	$259.1285	$259.13	$259.15	$259.10
7 purchase totals =	$1,161.99		$1,284.2581	$1,284.27	$1,284.30	$1,284.20