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	$79.43	13.495%	$90.1491	$90.15	$90.15	$90.10
Purchase #2	$35.60	7.757%	$38.3615	$38.36	$38.35	$38.40
Purchase #3	$6.52	12.643%	$7.3443	$7.34	$7.35	$7.30
Purchase #4	$108.80	4.790%	$114.0115	$114.01	$114.00	$114.00
Purchase #5	$219.64	4.334%	$229.1592	$229.16	$229.15	$229.20
Purchase #6	$113.89	8.644%	$123.7347	$123.73	$123.75	$123.70
Purchase #7	$18.72	4.775%	$19.6139	$19.61	$19.60	$19.60
7 purchase totals =	$582.60		$622.3742	$622.36	$622.35	$622.30