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	$136.49	3.673%	$141.5033	$141.50	$141.50	$141.50
Purchase #2	$32.37	13.329%	$36.6846	$36.68	$36.70	$36.70
Purchase #3	$156.72	8.143%	$169.4817	$169.48	$169.50	$169.50
Purchase #4	$48.62	6.572%	$51.8153	$51.82	$51.80	$51.80
Purchase #5	$39.67	9.371%	$43.3875	$43.39	$43.40	$43.40
Purchase #6	$61.90	8.123%	$66.9281	$66.93	$66.95	$66.90
Purchase #7	$57.34	5.647%	$60.578	$60.58	$60.60	$60.60
7 purchase totals =	$533.11		$570.3785	$570.38	$570.45	$570.40