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	$19.51	9.202%	$21.3053	$21.31	$21.30	$21.30
Purchase #2	$135.41	6.437%	$144.1263	$144.13	$144.15	$144.10
Purchase #3	$17.49	3.411%	$18.0866	$18.09	$18.10	$18.10
Purchase #4	$236.28	7.423%	$253.8191	$253.82	$253.80	$253.80
Purchase #5	$118.59	7.318%	$127.2684	$127.27	$127.25	$127.30
Purchase #6	$150.92	10.700%	$167.0684	$167.07	$167.05	$167.10
Purchase #7	$70.66	7.754%	$76.139	$76.14	$76.15	$76.10
7 purchase totals =	$748.86		$807.8131	$807.83	$807.80	$807.80