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	$217.79	4.523%	$227.6406	$227.64	$227.65	$227.60
Purchase #2	$50.83	9.420%	$55.6182	$55.62	$55.60	$55.60
Purchase #3	$40.94	4.246%	$42.6783	$42.68	$42.70	$42.70
Purchase #4	$141.50	13.557%	$160.6832	$160.68	$160.70	$160.70
Purchase #5	$75.47	3.631%	$78.2103	$78.21	$78.20	$78.20
Purchase #6	$41.90	10.618%	$46.3489	$46.35	$46.35	$46.30
Purchase #7	$72.48	13.266%	$82.0952	$82.10	$82.10	$82.10
7 purchase totals =	$640.91		$693.2747	$693.28	$693.30	$693.20