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	$129.46	3.622%	$134.149	$134.15	$134.15	$134.10
Purchase #2	$90.29	5.637%	$95.3796	$95.38	$95.40	$95.40
Purchase #3	$167.58	13.787%	$190.6843	$190.68	$190.70	$190.70
Purchase #4	$122.96	3.225%	$126.9255	$126.93	$126.95	$126.90
Purchase #5	$176.56	13.127%	$199.737	$199.74	$199.75	$199.70
Purchase #6	$95.31	10.788%	$105.592	$105.59	$105.60	$105.60
Purchase #7	$40.81	4.673%	$42.7171	$42.72	$42.70	$42.70
7 purchase totals =	$822.97		$895.1845	$895.19	$895.25	$895.10