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	$10.41	12.348%	$11.6954	$11.70	$11.70	$11.70
Purchase #2	$136.52	9.538%	$149.5413	$149.54	$149.55	$149.50
Purchase #3	$43.39	5.110%	$45.6072	$45.61	$45.60	$45.60
Purchase #4	$222.82	6.609%	$237.5462	$237.55	$237.55	$237.50
Purchase #5	$175.36	11.864%	$196.1647	$196.16	$196.15	$196.20
Purchase #6	$106.35	12.690%	$119.8458	$119.85	$119.85	$119.80
Purchase #7	$192.56	8.328%	$208.5964	$208.60	$208.60	$208.60
7 purchase totals =	$887.41		$968.9970	$969.01	$969.00	$968.90