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	$38.82	5.408%	$40.9194	$40.92	$40.90	$40.90
Purchase #2	$92.87	9.750%	$101.9248	$101.92	$101.90	$101.90
Purchase #3	$6.60	11.147%	$7.3357	$7.34	$7.35	$7.30
Purchase #4	$105.44	13.786%	$119.976	$119.98	$120.00	$120.00
Purchase #5	$179.52	8.671%	$195.0862	$195.09	$195.10	$195.10
Purchase #6	$52.67	13.154%	$59.5982	$59.60	$59.60	$59.60
Purchase #7	$51.25	4.254%	$53.4302	$53.43	$53.45	$53.40
7 purchase totals =	$527.17		$578.2705	$578.28	$578.30	$578.20