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	$7.63	8.741%	$8.2969	$8.30	$8.30	$8.30
Purchase #2	$59.54	5.489%	$62.8082	$62.81	$62.80	$62.80
Purchase #3	$132.39	4.458%	$138.2919	$138.29	$138.30	$138.30
Purchase #4	$97.65	5.766%	$103.2805	$103.28	$103.30	$103.30
Purchase #5	$11.86	3.729%	$12.3023	$12.30	$12.30	$12.30
Purchase #6	$33.42	12.694%	$37.6623	$37.66	$37.65	$37.70
Purchase #7	$74.51	5.516%	$78.62	$78.62	$78.60	$78.60
7 purchase totals =	$417.00		$441.2621	$441.26	$441.25	$441.30