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	$37.87	3.549%	$39.214	$39.21	$39.20	$39.20
Purchase #2	$247.45	7.598%	$266.2513	$266.25	$266.25	$266.30
Purchase #3	$96.43	13.536%	$109.4828	$109.48	$109.50	$109.50
Purchase #4	$192.36	8.375%	$208.4702	$208.47	$208.45	$208.50
Purchase #5	$134.78	13.208%	$152.5817	$152.58	$152.60	$152.60
Purchase #6	$9.40	4.869%	$9.8577	$9.86	$9.85	$9.90
Purchase #7	$119.61	3.352%	$123.6193	$123.62	$123.60	$123.60
7 purchase totals =	$837.90		$909.4770	$909.47	$909.45	$909.60