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	$90.46	11.560%	$100.9172	$100.92	$100.90	$100.90
Purchase #2	$72.85	12.189%	$81.7297	$81.73	$81.75	$81.70
Purchase #3	$250.71	9.796%	$275.2696	$275.27	$275.25	$275.30
Purchase #4	$205.56	4.636%	$215.0898	$215.09	$215.10	$215.10
Purchase #5	$85.71	13.464%	$97.25	$97.25	$97.25	$97.30
Purchase #6	$126.45	4.524%	$132.1706	$132.17	$132.15	$132.20
Purchase #7	$133.43	9.804%	$146.5115	$146.51	$146.50	$146.50
7 purchase totals =	$965.17		$1,048.9384	$1,048.94	$1,048.90	$1,049.00