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	$8.85	13.799%	$10.0712	$10.07	$10.05	$10.10
Purchase #2	$118.62	11.390%	$132.1308	$132.13	$132.15	$132.10
Purchase #3	$212.39	12.686%	$239.3338	$239.33	$239.35	$239.30
Purchase #4	$139.82	9.845%	$153.5853	$153.59	$153.60	$153.60
Purchase #5	$57.38	4.435%	$59.9248	$59.92	$59.90	$59.90
Purchase #6	$64.26	12.159%	$72.0734	$72.07	$72.05	$72.10
Purchase #7	$155.76	9.715%	$170.8921	$170.89	$170.90	$170.90
7 purchase totals =	$757.08		$838.0114	$838.00	$838.00	$838.00