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	$248.32	6.111%	$263.4948	$263.49	$263.50	$263.50
Purchase #2	$85.92	10.225%	$94.7053	$94.71	$94.70	$94.70
Purchase #3	$160.75	6.860%	$171.7775	$171.78	$171.80	$171.80
Purchase #4	$11.95	8.694%	$12.9889	$12.99	$13.00	$13.00
Purchase #5	$90.63	11.765%	$101.2926	$101.29	$101.30	$101.30
Purchase #6	$32.34	6.722%	$34.5139	$34.51	$34.50	$34.50
Purchase #7	$119.41	3.754%	$123.8927	$123.89	$123.90	$123.90
7 purchase totals =	$749.32		$802.6657	$802.66	$802.70	$802.70