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	$190.64	12.447%	$214.369	$214.37	$214.35	$214.40
Purchase #2	$145.71	6.763%	$155.5644	$155.56	$155.55	$155.60
Purchase #3	$36.99	10.508%	$40.8769	$40.88	$40.90	$40.90
Purchase #4	$232.70	9.727%	$255.3347	$255.33	$255.35	$255.30
Purchase #5	$134.72	7.859%	$145.3076	$145.31	$145.30	$145.30
Purchase #6	$118.40	12.687%	$133.4214	$133.42	$133.40	$133.40
Purchase #7	$59.31	11.602%	$66.1911	$66.19	$66.20	$66.20
7 purchase totals =	$918.47		$1,011.0651	$1,011.06	$1,011.05	$1,011.10