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	$106.80	12.705%	$120.3689	$120.37	$120.35	$120.40
Purchase #2	$22.64	13.618%	$25.7231	$25.72	$25.70	$25.70
Purchase #3	$169.51	9.743%	$186.0254	$186.03	$186.05	$186.00
Purchase #4	$79.39	13.683%	$90.2529	$90.25	$90.25	$90.30
Purchase #5	$170.29	13.680%	$193.5857	$193.59	$193.60	$193.60
Purchase #6	$158.47	13.222%	$179.4229	$179.42	$179.40	$179.40
Purchase #7	$31.37	3.263%	$32.3936	$32.39	$32.40	$32.40
7 purchase totals =	$738.47		$827.7725	$827.77	$827.75	$827.80