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	$92.37	11.679%	$103.1579	$103.16	$103.15	$103.20
Purchase #2	$112.41	5.281%	$118.3464	$118.35	$118.35	$118.30
Purchase #3	$112.35	13.266%	$127.2544	$127.25	$127.25	$127.30
Purchase #4	$69.27	10.520%	$76.5572	$76.56	$76.55	$76.60
Purchase #5	$143.51	8.358%	$155.5046	$155.50	$155.50	$155.50
Purchase #6	$29.40	7.152%	$31.5027	$31.50	$31.50	$31.50
Purchase #7	$181.32	9.592%	$198.7122	$198.71	$198.70	$198.70
7 purchase totals =	$740.63		$811.0354	$811.03	$811.00	$811.10