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	$122.58	13.476%	$139.0989	$139.10	$139.10	$139.10
Purchase #2	$144.91	6.545%	$154.3944	$154.39	$154.40	$154.40
Purchase #3	$173.77	6.734%	$185.4717	$185.47	$185.45	$185.50
Purchase #4	$148.68	3.449%	$153.808	$153.81	$153.80	$153.80
Purchase #5	$43.50	5.304%	$45.8072	$45.81	$45.80	$45.80
Purchase #6	$50.45	12.132%	$56.5706	$56.57	$56.55	$56.60
Purchase #7	$80.51	3.689%	$83.48	$83.48	$83.50	$83.50
7 purchase totals =	$764.40		$818.6308	$818.63	$818.60	$818.70