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	$77.58	13.148%	$87.7802	$87.78	$87.80	$87.80
Purchase #2	$77.93	4.630%	$81.5382	$81.54	$81.55	$81.50
Purchase #3	$37.28	9.748%	$40.9141	$40.91	$40.90	$40.90
Purchase #4	$66.48	4.620%	$69.5514	$69.55	$69.55	$69.60
Purchase #5	$42.78	10.688%	$47.3523	$47.35	$47.35	$47.40
Purchase #6	$154.35	6.638%	$164.5958	$164.60	$164.60	$164.60
Purchase #7	$90.41	10.207%	$99.6381	$99.64	$99.65	$99.60
7 purchase totals =	$546.81		$591.3701	$591.37	$591.40	$591.40