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	$59.26	13.595%	$67.3164	$67.32	$67.30	$67.30
Purchase #2	$56.42	5.789%	$59.6862	$59.69	$59.70	$59.70
Purchase #3	$6.85	11.158%	$7.6143	$7.61	$7.60	$7.60
Purchase #4	$226.40	9.315%	$247.4892	$247.49	$247.50	$247.50
Purchase #5	$183.84	4.189%	$191.5411	$191.54	$191.55	$191.50
Purchase #6	$134.79	9.689%	$147.8498	$147.85	$147.85	$147.80
Purchase #7	$50.57	4.674%	$52.9336	$52.93	$52.95	$52.90
7 purchase totals =	$718.13		$774.4306	$774.43	$774.45	$774.30