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	$80.33	5.868%	$85.0438	$85.04	$85.05	$85.00
Purchase #2	$227.71	13.360%	$258.1321	$258.13	$258.15	$258.10
Purchase #3	$155.46	5.844%	$164.5451	$164.55	$164.55	$164.50
Purchase #4	$127.77	7.788%	$137.7207	$137.72	$137.70	$137.70
Purchase #5	$149.71	5.853%	$158.4725	$158.47	$158.45	$158.50
Purchase #6	$29.25	12.607%	$32.9375	$32.94	$32.95	$32.90
Purchase #7	$112.49	5.747%	$118.9548	$118.95	$118.95	$119.00
7 purchase totals =	$882.72		$955.8065	$955.80	$955.80	$955.70