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	$148.64	11.800%	$166.1795	$166.18	$166.20	$166.20
Purchase #2	$122.58	9.839%	$134.6406	$134.64	$134.65	$134.60
Purchase #3	$213.70	5.665%	$225.8061	$225.81	$225.80	$225.80
Purchase #4	$9.80	10.706%	$10.8492	$10.85	$10.85	$10.80
Purchase #5	$131.59	9.448%	$144.0226	$144.02	$144.00	$144.00
Purchase #6	$89.85	11.183%	$99.8979	$99.90	$99.90	$99.90
Purchase #7	$172.34	10.397%	$190.2582	$190.26	$190.25	$190.30
7 purchase totals =	$888.50		$971.6541	$971.66	$971.65	$971.60