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	$42.29	5.405%	$44.5758	$44.58	$44.60	$44.60
Purchase #2	$232.96	8.327%	$252.3586	$252.36	$252.35	$252.40
Purchase #3	$189.66	5.545%	$200.1766	$200.18	$200.20	$200.20
Purchase #4	$233.98	9.546%	$256.3157	$256.32	$256.30	$256.30
Purchase #5	$128.85	10.656%	$142.5803	$142.58	$142.60	$142.60
Purchase #6	$153.38	7.106%	$164.2792	$164.28	$164.30	$164.30
Purchase #7	$38.77	3.250%	$40.03	$40.03	$40.05	$40.00
7 purchase totals =	$1,019.89		$1,100.3162	$1,100.33	$1,100.40	$1,100.40