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	$36.76	6.288%	$39.0715	$39.07	$39.05	$39.10
Purchase #2	$52.80	6.387%	$56.1723	$56.17	$56.15	$56.20
Purchase #3	$75.58	4.245%	$78.7884	$78.79	$78.80	$78.80
Purchase #4	$5.48	5.254%	$5.7679	$5.77	$5.75	$5.80
Purchase #5	$49.91	3.129%	$51.4717	$51.47	$51.45	$51.50
Purchase #6	$119.27	3.868%	$123.8834	$123.88	$123.90	$123.90
Purchase #7	$27.87	13.845%	$31.7286	$31.73	$31.75	$31.70
7 purchase totals =	$367.67		$386.8838	$386.88	$386.85	$387.00