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	$128.71	6.484%	$137.0556	$137.06	$137.05	$137.10
Purchase #2	$132.39	3.224%	$136.6583	$136.66	$136.65	$136.70
Purchase #3	$78.88	13.167%	$89.2661	$89.27	$89.25	$89.30
Purchase #4	$71.72	13.812%	$81.626	$81.63	$81.65	$81.60
Purchase #5	$30.27	10.574%	$33.4707	$33.47	$33.45	$33.50
Purchase #6	$138.60	7.686%	$149.2528	$149.25	$149.25	$149.30
Purchase #7	$115.49	11.504%	$128.776	$128.78	$128.80	$128.80
7 purchase totals =	$696.06		$756.1055	$756.12	$756.10	$756.30