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	$27.99	6.154%	$29.7125	$29.71	$29.70	$29.70
Purchase #2	$148.30	6.264%	$157.5895	$157.59	$157.60	$157.60
Purchase #3	$222.34	11.708%	$248.3716	$248.37	$248.35	$248.40
Purchase #4	$187.98	6.666%	$200.5107	$200.51	$200.50	$200.50
Purchase #5	$38.79	9.815%	$42.5972	$42.60	$42.60	$42.60
Purchase #6	$146.59	4.723%	$153.5134	$153.51	$153.50	$153.50
Purchase #7	$30.32	4.722%	$31.7517	$31.75	$31.75	$31.80
7 purchase totals =	$802.31		$864.0466	$864.04	$864.00	$864.10