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	$235.29	11.864%	$263.2048	$263.20	$263.20	$263.20
Purchase #2	$25.50	11.433%	$28.4154	$28.42	$28.40	$28.40
Purchase #3	$131.75	7.375%	$141.4666	$141.47	$141.45	$141.50
Purchase #4	$155.28	13.520%	$176.2739	$176.27	$176.25	$176.30
Purchase #5	$90.32	10.707%	$99.9906	$99.99	$100.00	$100.00
Purchase #6	$138.31	3.750%	$143.4966	$143.50	$143.50	$143.50
Purchase #7	$172.88	13.382%	$196.0148	$196.01	$196.00	$196.00
7 purchase totals =	$949.33		$1,048.8627	$1,048.86	$1,048.80	$1,048.90