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	$130.56	13.600%	$148.3162	$148.32	$148.30	$148.30
Purchase #2	$109.83	8.366%	$119.0184	$119.02	$119.00	$119.00
Purchase #3	$71.92	12.142%	$80.6525	$80.65	$80.65	$80.70
Purchase #4	$117.33	5.249%	$123.4887	$123.49	$123.50	$123.50
Purchase #5	$34.38	11.407%	$38.3017	$38.30	$38.30	$38.30
Purchase #6	$224.98	7.128%	$241.0166	$241.02	$241.00	$241.00
Purchase #7	$153.46	5.621%	$162.086	$162.09	$162.10	$162.10
7 purchase totals =	$842.46		$912.8801	$912.89	$912.85	$912.90