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	$114.43	12.629%	$128.8814	$128.88	$128.90	$128.90
Purchase #2	$57.48	3.648%	$59.5769	$59.58	$59.60	$59.60
Purchase #3	$107.61	3.153%	$111.0029	$111.00	$111.00	$111.00
Purchase #4	$54.62	7.786%	$58.8727	$58.87	$58.85	$58.90
Purchase #5	$170.91	4.536%	$178.6625	$178.66	$178.65	$178.70
Purchase #6	$18.92	8.679%	$20.5621	$20.56	$20.55	$20.60
Purchase #7	$248.61	9.414%	$272.0141	$272.01	$272.00	$272.00
7 purchase totals =	$772.58		$829.5726	$829.56	$829.55	$829.70