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	$38.48	4.688%	$40.2839	$40.28	$40.30	$40.30
Purchase #2	$103.76	7.149%	$111.1778	$111.18	$111.20	$111.20
Purchase #3	$155.64	5.867%	$164.7714	$164.77	$164.75	$164.80
Purchase #4	$100.72	7.385%	$108.1582	$108.16	$108.15	$108.20
Purchase #5	$102.56	9.452%	$112.254	$112.25	$112.25	$112.30
Purchase #6	$190.88	9.483%	$208.9812	$208.98	$209.00	$209.00
Purchase #7	$153.72	12.516%	$172.9596	$172.96	$172.95	$173.00
7 purchase totals =	$845.76		$918.5861	$918.58	$918.60	$918.80