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	$13.57	13.388%	$15.3868	$15.39	$15.40	$15.40
Purchase #2	$131.52	10.787%	$145.7071	$145.71	$145.70	$145.70
Purchase #3	$71.74	11.591%	$80.0554	$80.06	$80.05	$80.10
Purchase #4	$169.80	9.496%	$185.9242	$185.92	$185.90	$185.90
Purchase #5	$116.91	9.677%	$128.2234	$128.22	$128.20	$128.20
Purchase #6	$65.30	10.581%	$72.2094	$72.21	$72.20	$72.20
Purchase #7	$50.57	4.546%	$52.8689	$52.87	$52.85	$52.90
7 purchase totals =	$619.41		$680.3752	$680.38	$680.30	$680.40