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	$250.38	10.732%	$277.2508	$277.25	$277.25	$277.30
Purchase #2	$184.81	8.470%	$200.4634	$200.46	$200.45	$200.50
Purchase #3	$48.31	11.833%	$54.0265	$54.03	$54.05	$54.00
Purchase #4	$72.64	8.617%	$78.8994	$78.90	$78.90	$78.90
Purchase #5	$60.44	10.491%	$66.7808	$66.78	$66.80	$66.80
Purchase #6	$41.84	3.286%	$43.2149	$43.21	$43.20	$43.20
Purchase #7	$109.65	13.727%	$124.7017	$124.70	$124.70	$124.70
7 purchase totals =	$768.07		$845.3375	$845.33	$845.35	$845.40