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	$160.50	5.230%	$168.8942	$168.89	$168.90	$168.90
Purchase #2	$80.95	12.103%	$90.7474	$90.75	$90.75	$90.70
Purchase #3	$233.45	3.865%	$242.4728	$242.47	$242.45	$242.50
Purchase #4	$35.47	11.520%	$39.5561	$39.56	$39.55	$39.60
Purchase #5	$199.81	13.745%	$227.2739	$227.27	$227.25	$227.30
Purchase #6	$203.91	11.364%	$227.0823	$227.08	$227.10	$227.10
Purchase #7	$171.47	9.292%	$187.403	$187.40	$187.40	$187.40
7 purchase totals =	$1,085.56		$1,183.4297	$1,183.42	$1,183.40	$1,183.50