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	$241.88	9.614%	$265.1343	$265.13	$265.15	$265.10
Purchase #2	$81.84	10.874%	$90.7393	$90.74	$90.75	$90.70
Purchase #3	$100.68	13.824%	$114.598	$114.60	$114.60	$114.60
Purchase #4	$208.28	7.750%	$224.4217	$224.42	$224.40	$224.40
Purchase #5	$131.32	4.782%	$137.5997	$137.60	$137.60	$137.60
Purchase #6	$35.75	13.744%	$40.6635	$40.66	$40.65	$40.70
Purchase #7	$73.39	13.774%	$83.4987	$83.50	$83.50	$83.50
7 purchase totals =	$873.14		$956.6552	$956.65	$956.65	$956.60