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	$24.57	12.268%	$27.5842	$27.58	$27.60	$27.60
Purchase #2	$244.84	4.678%	$256.2936	$256.29	$256.30	$256.30
Purchase #3	$21.41	5.775%	$22.6464	$22.65	$22.65	$22.60
Purchase #4	$30.74	5.334%	$32.3797	$32.38	$32.40	$32.40
Purchase #5	$230.74	13.764%	$262.4991	$262.50	$262.50	$262.50
Purchase #6	$67.47	7.787%	$72.7239	$72.72	$72.70	$72.70
Purchase #7	$76.39	5.328%	$80.4601	$80.46	$80.45	$80.50
7 purchase totals =	$696.16		$754.5870	$754.58	$754.60	$754.60