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	$45.47	13.466%	$51.593	$51.59	$51.60	$51.60
Purchase #2	$39.71	9.505%	$43.4844	$43.48	$43.50	$43.50
Purchase #3	$188.96	8.186%	$204.4283	$204.43	$204.45	$204.40
Purchase #4	$113.28	12.327%	$127.244	$127.24	$127.25	$127.20
Purchase #5	$60.25	8.347%	$65.2791	$65.28	$65.30	$65.30
Purchase #6	$93.52	11.141%	$103.9391	$103.94	$103.95	$103.90
Purchase #7	$35.95	6.131%	$38.1541	$38.15	$38.15	$38.20
7 purchase totals =	$577.14		$634.1220	$634.11	$634.20	$634.10