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	$95.73	4.131%	$99.6846	$99.68	$99.70	$99.70
Purchase #2	$70.40	7.188%	$75.4604	$75.46	$75.45	$75.50
Purchase #3	$160.78	6.269%	$170.8593	$170.86	$170.85	$170.90
Purchase #4	$73.83	12.117%	$82.776	$82.78	$82.80	$82.80
Purchase #5	$92.85	10.489%	$102.589	$102.59	$102.60	$102.60
Purchase #6	$233.59	5.521%	$246.4865	$246.49	$246.50	$246.50
Purchase #7	$41.40	8.635%	$44.9749	$44.97	$44.95	$45.00
7 purchase totals =	$768.58		$822.8307	$822.83	$822.85	$823.00