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	$88.89	11.671%	$99.2644	$99.26	$99.25	$99.30
Purchase #2	$7.92	5.786%	$8.3783	$8.38	$8.40	$8.40
Purchase #3	$153.67	6.392%	$163.4926	$163.49	$163.50	$163.50
Purchase #4	$31.34	3.658%	$32.4864	$32.49	$32.50	$32.50
Purchase #5	$125.60	8.396%	$136.1454	$136.15	$136.15	$136.10
Purchase #6	$68.52	13.561%	$77.812	$77.81	$77.80	$77.80
Purchase #7	$37.80	10.791%	$41.879	$41.88	$41.90	$41.90
7 purchase totals =	$513.74		$559.4581	$559.46	$559.50	$559.50