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	$38.76	6.233%	$41.1759	$41.18	$41.20	$41.20
Purchase #2	$246.29	13.837%	$280.3691	$280.37	$280.35	$280.40
Purchase #3	$108.29	7.245%	$116.1356	$116.14	$116.15	$116.10
Purchase #4	$33.71	12.597%	$37.9564	$37.96	$37.95	$38.00
Purchase #5	$96.66	6.617%	$103.056	$103.06	$103.05	$103.10
Purchase #6	$146.33	9.757%	$160.6074	$160.61	$160.60	$160.60
Purchase #7	$152.92	3.359%	$158.0566	$158.06	$158.05	$158.10
7 purchase totals =	$822.96		$897.3570	$897.38	$897.35	$897.50