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	$15.43	13.188%	$17.4649	$17.46	$17.45	$17.50
Purchase #2	$38.46	13.340%	$43.5906	$43.59	$43.60	$43.60
Purchase #3	$95.73	3.824%	$99.3907	$99.39	$99.40	$99.40
Purchase #4	$130.42	7.640%	$140.3841	$140.38	$140.40	$140.40
Purchase #5	$51.36	8.473%	$55.7117	$55.71	$55.70	$55.70
Purchase #6	$49.38	4.242%	$51.4747	$51.47	$51.45	$51.50
Purchase #7	$230.52	12.716%	$259.8329	$259.83	$259.85	$259.80
7 purchase totals =	$611.30		$667.8496	$667.83	$667.85	$667.90