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	$50.56	8.871%	$55.0452	$55.05	$55.05	$55.00
Purchase #2	$121.94	8.670%	$132.5122	$132.51	$132.50	$132.50
Purchase #3	$197.39	8.211%	$213.5977	$213.60	$213.60	$213.60
Purchase #4	$230.45	13.400%	$261.3303	$261.33	$261.35	$261.30
Purchase #5	$28.49	8.821%	$31.0031	$31.00	$31.00	$31.00
Purchase #6	$101.85	3.460%	$105.374	$105.37	$105.35	$105.40
Purchase #7	$184.57	3.259%	$190.5851	$190.59	$190.60	$190.60
7 purchase totals =	$915.25		$989.4476	$989.45	$989.45	$989.40