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	$14.32	6.144%	$15.1998	$15.20	$15.20	$15.20
Purchase #2	$171.87	13.208%	$194.5706	$194.57	$194.55	$194.60
Purchase #3	$16.58	11.603%	$18.5038	$18.50	$18.50	$18.50
Purchase #4	$146.51	4.792%	$153.5308	$153.53	$153.55	$153.50
Purchase #5	$86.55	3.560%	$89.6312	$89.63	$89.65	$89.60
Purchase #6	$213.98	4.818%	$224.2896	$224.29	$224.30	$224.30
Purchase #7	$170.60	9.833%	$187.3751	$187.38	$187.40	$187.40
7 purchase totals =	$820.41		$883.1009	$883.10	$883.15	$883.10