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	$62.82	5.264%	$66.1268	$66.13	$66.15	$66.10
Purchase #2	$216.33	10.263%	$238.5319	$238.53	$238.55	$238.50
Purchase #3	$216.74	12.294%	$243.386	$243.39	$243.40	$243.40
Purchase #4	$52.72	12.776%	$59.4555	$59.46	$59.45	$59.50
Purchase #5	$74.46	10.237%	$82.0825	$82.08	$82.10	$82.10
Purchase #6	$219.77	3.409%	$227.262	$227.26	$227.25	$227.30
Purchase #7	$73.31	11.105%	$81.4511	$81.45	$81.45	$81.50
7 purchase totals =	$916.15		$998.2958	$998.30	$998.35	$998.40