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	$34.94	10.459%	$38.5944	$38.59	$38.60	$38.60
Purchase #2	$199.43	9.338%	$218.0528	$218.05	$218.05	$218.10
Purchase #3	$195.51	12.166%	$219.2957	$219.30	$219.30	$219.30
Purchase #4	$12.49	11.190%	$13.8876	$13.89	$13.90	$13.90
Purchase #5	$99.78	5.785%	$105.5523	$105.55	$105.55	$105.60
Purchase #6	$166.40	8.795%	$181.0349	$181.03	$181.05	$181.00
Purchase #7	$243.52	11.829%	$272.326	$272.33	$272.35	$272.30
7 purchase totals =	$952.07		$1,048.7437	$1,048.74	$1,048.80	$1,048.80