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	$34.83	10.768%	$38.5805	$38.58	$38.60	$38.60
Purchase #2	$104.38	13.357%	$118.322	$118.32	$118.30	$118.30
Purchase #3	$99.65	9.834%	$109.4496	$109.45	$109.45	$109.40
Purchase #4	$123.93	4.493%	$129.4982	$129.50	$129.50	$129.50
Purchase #5	$228.54	7.723%	$246.1901	$246.19	$246.20	$246.20
Purchase #6	$200.28	13.634%	$227.5862	$227.59	$227.60	$227.60
Purchase #7	$161.56	12.298%	$181.4286	$181.43	$181.45	$181.40
7 purchase totals =	$953.17		$1,051.0552	$1,051.06	$1,051.10	$1,051.00