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	$73.25	13.415%	$83.0765	$83.08	$83.10	$83.10
Purchase #2	$222.60	9.581%	$243.9273	$243.93	$243.95	$243.90
Purchase #3	$183.55	3.762%	$190.4552	$190.46	$190.45	$190.50
Purchase #4	$186.96	5.291%	$196.8521	$196.85	$196.85	$196.90
Purchase #5	$37.36	10.778%	$41.3867	$41.39	$41.40	$41.40
Purchase #6	$99.78	8.563%	$108.3242	$108.32	$108.30	$108.30
Purchase #7	$178.73	3.728%	$185.3931	$185.39	$185.40	$185.40
7 purchase totals =	$982.23		$1,049.4151	$1,049.42	$1,049.45	$1,049.50