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	$18.37	12.152%	$20.6023	$20.60	$20.60	$20.60
Purchase #2	$45.45	7.604%	$48.906	$48.91	$48.90	$48.90
Purchase #3	$40.42	11.487%	$45.063	$45.06	$45.05	$45.10
Purchase #4	$148.71	11.136%	$165.2703	$165.27	$165.25	$165.30
Purchase #5	$165.89	8.787%	$180.4668	$180.47	$180.45	$180.50
Purchase #6	$196.79	10.492%	$217.4372	$217.44	$217.45	$217.40
Purchase #7	$145.91	9.290%	$159.465	$159.47	$159.45	$159.50
7 purchase totals =	$761.54		$837.2106	$837.22	$837.15	$837.30