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	$54.52	8.571%	$59.1929	$59.19	$59.20	$59.20
Purchase #2	$44.40	7.815%	$47.8699	$47.87	$47.85	$47.90
Purchase #3	$25.47	8.640%	$27.6706	$27.67	$27.65	$27.70
Purchase #4	$77.76	5.747%	$82.2289	$82.23	$82.25	$82.20
Purchase #5	$80.86	8.611%	$87.8229	$87.82	$87.80	$87.80
Purchase #6	$119.75	13.705%	$136.1617	$136.16	$136.15	$136.20
Purchase #7	$167.47	6.294%	$178.0106	$178.01	$178.00	$178.00
7 purchase totals =	$570.23		$618.9575	$618.95	$618.90	$619.00