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	$68.69	13.423%	$77.9103	$77.91	$77.90	$77.90
Purchase #2	$192.82	11.304%	$214.6164	$214.62	$214.60	$214.60
Purchase #3	$94.57	5.631%	$99.8952	$99.90	$99.90	$99.90
Purchase #4	$153.61	13.853%	$174.8896	$174.89	$174.90	$174.90
Purchase #5	$137.80	7.762%	$148.496	$148.50	$148.50	$148.50
Purchase #6	$120.31	11.321%	$133.9303	$133.93	$133.95	$133.90
Purchase #7	$127.61	8.388%	$138.3139	$138.31	$138.30	$138.30
7 purchase totals =	$895.41		$988.0517	$988.06	$988.05	$988.00