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	$72.25	8.607%	$78.4686	$78.47	$78.45	$78.50
Purchase #2	$164.95	12.373%	$185.3593	$185.36	$185.35	$185.40
Purchase #3	$40.80	8.358%	$44.2101	$44.21	$44.20	$44.20
Purchase #4	$6.75	12.335%	$7.5826	$7.58	$7.60	$7.60
Purchase #5	$109.70	12.853%	$123.7997	$123.80	$123.80	$123.80
Purchase #6	$161.40	9.488%	$176.7136	$176.71	$176.70	$176.70
Purchase #7	$248.32	9.254%	$271.2995	$271.30	$271.30	$271.30
7 purchase totals =	$804.17		$887.4334	$887.43	$887.40	$887.50