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	$209.78	10.659%	$232.1405	$232.14	$232.15	$232.10
Purchase #2	$148.88	9.210%	$162.5918	$162.59	$162.60	$162.60
Purchase #3	$34.54	10.298%	$38.0969	$38.10	$38.10	$38.10
Purchase #4	$163.87	6.755%	$174.9394	$174.94	$174.95	$174.90
Purchase #5	$111.92	4.262%	$116.69	$116.69	$116.70	$116.70
Purchase #6	$63.37	12.337%	$71.188	$71.19	$71.20	$71.20
Purchase #7	$21.56	13.109%	$24.3863	$24.39	$24.40	$24.40
7 purchase totals =	$753.92		$820.0329	$820.04	$820.10	$820.00