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	$129.30	3.306%	$133.5747	$133.57	$133.55	$133.60
Purchase #2	$211.51	11.783%	$236.4322	$236.43	$236.45	$236.40
Purchase #3	$196.36	9.726%	$215.458	$215.46	$215.45	$215.50
Purchase #4	$25.91	4.459%	$27.0653	$27.07	$27.05	$27.10
Purchase #5	$74.91	9.643%	$82.1336	$82.13	$82.15	$82.10
Purchase #6	$61.82	6.130%	$65.6096	$65.61	$65.60	$65.60
Purchase #7	$18.72	8.536%	$20.3179	$20.32	$20.30	$20.30
7 purchase totals =	$718.53		$780.5913	$780.59	$780.55	$780.60