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	$42.79	9.243%	$46.7451	$46.75	$46.75	$46.70
Purchase #2	$29.27	12.619%	$32.9636	$32.96	$32.95	$33.00
Purchase #3	$50.81	7.636%	$54.6899	$54.69	$54.70	$54.70
Purchase #4	$157.73	9.333%	$172.4509	$172.45	$172.45	$172.50
Purchase #5	$143.36	13.622%	$162.8885	$162.89	$162.90	$162.90
Purchase #6	$95.52	4.152%	$99.486	$99.49	$99.50	$99.50
Purchase #7	$29.75	4.339%	$31.0409	$31.04	$31.05	$31.00
7 purchase totals =	$549.23		$600.2649	$600.27	$600.30	$600.30