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	$138.81	10.638%	$153.5766	$153.58	$153.60	$153.60
Purchase #2	$31.91	10.285%	$35.1919	$35.19	$35.20	$35.20
Purchase #3	$134.28	11.791%	$150.113	$150.11	$150.10	$150.10
Purchase #4	$29.43	7.154%	$31.5354	$31.54	$31.55	$31.50
Purchase #5	$82.60	12.769%	$93.1472	$93.15	$93.15	$93.10
Purchase #6	$235.59	3.509%	$243.8569	$243.86	$243.85	$243.90
Purchase #7	$71.51	10.487%	$79.0093	$79.01	$79.00	$79.00
7 purchase totals =	$724.13		$786.4303	$786.44	$786.45	$786.40