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	$160.73	13.411%	$182.2855	$182.29	$182.30	$182.30
Purchase #2	$114.80	12.285%	$128.9032	$128.90	$128.90	$128.90
Purchase #3	$58.44	6.515%	$62.2474	$62.25	$62.25	$62.20
Purchase #4	$50.60	7.113%	$54.1992	$54.20	$54.20	$54.20
Purchase #5	$52.46	13.313%	$59.444	$59.44	$59.45	$59.40
Purchase #6	$48.66	5.231%	$51.2054	$51.21	$51.20	$51.20
Purchase #7	$38.40	13.695%	$43.6589	$43.66	$43.65	$43.70
7 purchase totals =	$524.09		$581.9436	$581.95	$581.95	$581.90