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	$17.43	10.812%	$19.3145	$19.31	$19.30	$19.30
Purchase #2	$17.80	5.645%	$18.8048	$18.80	$18.80	$18.80
Purchase #3	$78.38	10.679%	$86.7502	$86.75	$86.75	$86.80
Purchase #4	$38.61	13.536%	$43.8362	$43.84	$43.85	$43.80
Purchase #5	$158.53	6.566%	$168.9391	$168.94	$168.95	$168.90
Purchase #6	$97.56	6.113%	$103.5238	$103.52	$103.50	$103.50
Purchase #7	$183.79	7.441%	$197.4658	$197.47	$197.45	$197.50
7 purchase totals =	$592.10		$638.6344	$638.63	$638.60	$638.60