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	$10.37	11.673%	$11.5805	$11.58	$11.60	$11.60
Purchase #2	$33.47	12.515%	$37.6588	$37.66	$37.65	$37.70
Purchase #3	$7.50	10.268%	$8.2701	$8.27	$8.25	$8.30
Purchase #4	$42.43	13.634%	$48.2149	$48.21	$48.20	$48.20
Purchase #5	$52.63	3.470%	$54.4563	$54.46	$54.45	$54.50
Purchase #6	$242.53	12.758%	$273.472	$273.47	$273.45	$273.50
Purchase #7	$93.77	10.109%	$103.2492	$103.25	$103.25	$103.20
7 purchase totals =	$482.70		$536.9018	$536.90	$536.85	$537.00