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	$20.65	9.784%	$22.6704	$22.67	$22.65	$22.70
Purchase #2	$225.55	10.627%	$249.5192	$249.52	$249.50	$249.50
Purchase #3	$230.92	10.684%	$255.5915	$255.59	$255.60	$255.60
Purchase #4	$103.59	5.557%	$109.3465	$109.35	$109.35	$109.30
Purchase #5	$15.47	11.808%	$17.2967	$17.30	$17.30	$17.30
Purchase #6	$237.71	7.760%	$256.1563	$256.16	$256.15	$256.20
Purchase #7	$29.44	9.200%	$32.1485	$32.15	$32.15	$32.10
7 purchase totals =	$863.33		$942.7291	$942.74	$942.70	$942.70