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	$34.57	11.747%	$38.6309	$38.63	$38.65	$38.60
Purchase #2	$55.74	4.777%	$58.4027	$58.40	$58.40	$58.40
Purchase #3	$175.61	10.597%	$194.2194	$194.22	$194.20	$194.20
Purchase #4	$71.49	9.299%	$78.1379	$78.14	$78.15	$78.10
Purchase #5	$13.68	5.686%	$14.4578	$14.46	$14.45	$14.50
Purchase #6	$31.56	3.329%	$32.6106	$32.61	$32.60	$32.60
Purchase #7	$139.59	11.627%	$155.8201	$155.82	$155.80	$155.80
7 purchase totals =	$522.24		$572.2794	$572.28	$572.25	$572.20