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	$51.68	7.138%	$55.3689	$55.37	$55.35	$55.40
Purchase #2	$107.53	8.766%	$116.9561	$116.96	$116.95	$117.00
Purchase #3	$144.57	4.394%	$150.9224	$150.92	$150.90	$150.90
Purchase #4	$104.45	6.871%	$111.6268	$111.63	$111.65	$111.60
Purchase #5	$216.33	10.186%	$238.3654	$238.37	$238.35	$238.40
Purchase #6	$201.38	8.771%	$219.043	$219.04	$219.05	$219.00
Purchase #7	$38.58	12.437%	$43.3782	$43.38	$43.40	$43.40
7 purchase totals =	$864.52		$935.6608	$935.67	$935.65	$935.70