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	$248.96	11.276%	$277.0327	$277.03	$277.05	$277.00
Purchase #2	$66.43	7.588%	$71.4707	$71.47	$71.45	$71.50
Purchase #3	$234.83	7.508%	$252.461	$252.46	$252.45	$252.50
Purchase #4	$37.50	12.323%	$42.1211	$42.12	$42.10	$42.10
Purchase #5	$217.31	11.305%	$241.8769	$241.88	$241.90	$241.90
Purchase #6	$17.82	13.703%	$20.2619	$20.26	$20.25	$20.30
Purchase #7	$30.44	11.167%	$33.8392	$33.84	$33.85	$33.80
7 purchase totals =	$853.29		$939.0635	$939.06	$939.05	$939.10