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	$11.29	13.852%	$12.8539	$12.85	$12.85	$12.90
Purchase #2	$121.42	13.503%	$137.8153	$137.82	$137.80	$137.80
Purchase #3	$202.94	10.504%	$224.2568	$224.26	$224.25	$224.30
Purchase #4	$38.33	5.812%	$40.5577	$40.56	$40.55	$40.60
Purchase #5	$16.66	9.605%	$18.2602	$18.26	$18.25	$18.30
Purchase #6	$36.39	5.216%	$38.2881	$38.29	$38.30	$38.30
Purchase #7	$98.36	7.611%	$105.8462	$105.85	$105.85	$105.80
7 purchase totals =	$525.39		$577.8782	$577.89	$577.85	$578.00