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	$100.43	3.256%	$103.7	$103.70	$103.70	$103.70
Purchase #2	$141.67	12.120%	$158.8404	$158.84	$158.85	$158.80
Purchase #3	$109.39	12.607%	$123.1808	$123.18	$123.20	$123.20
Purchase #4	$231.35	4.556%	$241.8903	$241.89	$241.90	$241.90
Purchase #5	$71.75	13.528%	$81.4563	$81.46	$81.45	$81.50
Purchase #6	$75.46	8.268%	$81.699	$81.70	$81.70	$81.70
Purchase #7	$162.48	7.280%	$174.3085	$174.31	$174.30	$174.30
7 purchase totals =	$892.53		$965.0753	$965.08	$965.10	$965.10