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	$30.66	12.429%	$34.4707	$34.47	$34.45	$34.50
Purchase #2	$58.95	12.590%	$66.3718	$66.37	$66.35	$66.40
Purchase #3	$16.92	5.872%	$17.9135	$17.91	$17.90	$17.90
Purchase #4	$38.95	4.605%	$40.7436	$40.74	$40.75	$40.70
Purchase #5	$187.86	3.108%	$193.6987	$193.70	$193.70	$193.70
Purchase #6	$144.77	4.524%	$151.3194	$151.32	$151.30	$151.30
Purchase #7	$150.41	8.260%	$162.8339	$162.83	$162.85	$162.80
7 purchase totals =	$628.52		$667.3516	$667.34	$667.30	$667.30