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	$82.62	9.520%	$90.4854	$90.49	$90.50	$90.50
Purchase #2	$48.55	8.538%	$52.6952	$52.70	$52.70	$52.70
Purchase #3	$68.40	6.391%	$72.7714	$72.77	$72.75	$72.80
Purchase #4	$20.59	3.659%	$21.3434	$21.34	$21.35	$21.30
Purchase #5	$185.65	5.729%	$196.2859	$196.29	$196.30	$196.30
Purchase #6	$41.71	4.474%	$43.5761	$43.58	$43.60	$43.60
Purchase #7	$74.34	9.311%	$81.2618	$81.26	$81.25	$81.30
7 purchase totals =	$521.86		$558.4192	$558.43	$558.45	$558.50