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	$17.30	10.118%	$19.0504	$19.05	$19.05	$19.10
Purchase #2	$146.45	12.768%	$165.1487	$165.15	$165.15	$165.10
Purchase #3	$247.55	12.219%	$277.7981	$277.80	$277.80	$277.80
Purchase #4	$77.77	11.734%	$86.8955	$86.90	$86.90	$86.90
Purchase #5	$89.29	13.214%	$101.0888	$101.09	$101.10	$101.10
Purchase #6	$88.42	13.837%	$100.6547	$100.65	$100.65	$100.70
Purchase #7	$137.35	9.298%	$150.1208	$150.12	$150.10	$150.10
7 purchase totals =	$804.13		$900.7570	$900.76	$900.75	$900.80