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	$88.92	12.706%	$100.2182	$100.22	$100.20	$100.20
Purchase #2	$95.77	9.784%	$105.1401	$105.14	$105.15	$105.10
Purchase #3	$208.72	3.224%	$215.4491	$215.45	$215.45	$215.40
Purchase #4	$103.44	12.271%	$116.1331	$116.13	$116.15	$116.10
Purchase #5	$123.63	6.828%	$132.0715	$132.07	$132.05	$132.10
Purchase #6	$16.90	11.534%	$18.8492	$18.85	$18.85	$18.80
Purchase #7	$232.43	13.255%	$263.2386	$263.24	$263.25	$263.20
7 purchase totals =	$869.81		$951.0998	$951.10	$951.10	$950.90