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	$59.84	11.600%	$66.7814	$66.78	$66.80	$66.80
Purchase #2	$231.47	11.761%	$258.6932	$258.69	$258.70	$258.70
Purchase #3	$34.89	8.185%	$37.7457	$37.75	$37.75	$37.70
Purchase #4	$41.66	9.312%	$45.5394	$45.54	$45.55	$45.50
Purchase #5	$172.67	9.324%	$188.7698	$188.77	$188.75	$188.80
Purchase #6	$41.79	9.465%	$45.7454	$45.75	$45.75	$45.70
Purchase #7	$30.95	11.758%	$34.5891	$34.59	$34.60	$34.60
7 purchase totals =	$613.27		$677.8640	$677.87	$677.90	$677.80