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	$100.76	10.770%	$111.6119	$111.61	$111.60	$111.60
Purchase #2	$43.25	8.816%	$47.0629	$47.06	$47.05	$47.10
Purchase #3	$82.77	12.167%	$92.8406	$92.84	$92.85	$92.80
Purchase #4	$95.98	6.133%	$101.8665	$101.87	$101.85	$101.90
Purchase #5	$154.87	5.470%	$163.3414	$163.34	$163.35	$163.30
Purchase #6	$77.90	4.229%	$81.1944	$81.19	$81.20	$81.20
Purchase #7	$105.80	6.731%	$112.9214	$112.92	$112.90	$112.90
7 purchase totals =	$661.33		$710.8391	$710.83	$710.80	$710.80