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	$24.31	12.676%	$27.3915	$27.39	$27.40	$27.40
Purchase #2	$140.68	9.337%	$153.8153	$153.82	$153.80	$153.80
Purchase #3	$20.39	4.277%	$21.2621	$21.26	$21.25	$21.30
Purchase #4	$231.25	6.688%	$246.716	$246.72	$246.70	$246.70
Purchase #5	$233.93	7.106%	$250.5531	$250.55	$250.55	$250.60
Purchase #6	$57.45	3.566%	$59.4987	$59.50	$59.50	$59.50
Purchase #7	$120.77	13.738%	$137.3614	$137.36	$137.35	$137.40
7 purchase totals =	$828.78		$896.5981	$896.60	$896.55	$896.70