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	$56.72	7.853%	$61.1742	$61.17	$61.15	$61.20
Purchase #2	$211.41	4.684%	$221.3124	$221.31	$221.30	$221.30
Purchase #3	$178.41	12.381%	$200.4989	$200.50	$200.50	$200.50
Purchase #4	$28.86	12.382%	$32.4334	$32.43	$32.45	$32.40
Purchase #5	$104.47	7.406%	$112.207	$112.21	$112.20	$112.20
Purchase #6	$117.35	13.751%	$133.4868	$133.49	$133.50	$133.50
Purchase #7	$61.86	7.295%	$66.3727	$66.37	$66.35	$66.40
7 purchase totals =	$759.08		$827.4854	$827.48	$827.45	$827.50