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	$139.80	11.206%	$155.466	$155.47	$155.45	$155.50
Purchase #2	$53.71	11.352%	$59.8072	$59.81	$59.80	$59.80
Purchase #3	$26.46	9.588%	$28.997	$29.00	$29.00	$29.00
Purchase #4	$79.83	13.434%	$90.5544	$90.55	$90.55	$90.60
Purchase #5	$29.68	12.335%	$33.341	$33.34	$33.35	$33.30
Purchase #6	$212.34	8.156%	$229.6585	$229.66	$229.65	$229.70
Purchase #7	$240.45	3.795%	$249.5751	$249.58	$249.60	$249.60
7 purchase totals =	$782.27		$847.3992	$847.41	$847.40	$847.50