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	$91.54	9.432%	$100.1741	$100.17	$100.15	$100.20
Purchase #2	$97.94	11.177%	$108.8868	$108.89	$108.90	$108.90
Purchase #3	$143.36	10.841%	$158.9017	$158.90	$158.90	$158.90
Purchase #4	$214.97	10.348%	$237.2151	$237.22	$237.20	$237.20
Purchase #5	$230.50	5.206%	$242.4998	$242.50	$242.50	$242.50
Purchase #6	$67.25	7.270%	$72.1391	$72.14	$72.15	$72.10
Purchase #7	$17.85	12.288%	$20.0434	$20.04	$20.05	$20.00
7 purchase totals =	$863.41		$939.8600	$939.86	$939.85	$939.80