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	$70.91	10.517%	$78.3676	$78.37	$78.35	$78.40
Purchase #2	$45.83	6.167%	$48.6563	$48.66	$48.65	$48.70
Purchase #3	$62.28	10.185%	$68.6232	$68.62	$68.60	$68.60
Purchase #4	$99.30	12.215%	$111.4295	$111.43	$111.45	$111.40
Purchase #5	$151.83	6.368%	$161.4985	$161.50	$161.50	$161.50
Purchase #6	$13.55	6.407%	$14.4181	$14.42	$14.40	$14.40
Purchase #7	$186.29	12.755%	$210.0513	$210.05	$210.05	$210.10
7 purchase totals =	$629.99		$693.0445	$693.05	$693.00	$693.10