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	$131.94	3.835%	$136.9999	$137.00	$137.00	$137.00
Purchase #2	$17.54	4.834%	$18.3879	$18.39	$18.40	$18.40
Purchase #3	$152.94	9.461%	$167.4097	$167.41	$167.40	$167.40
Purchase #4	$96.37	3.439%	$99.6842	$99.68	$99.70	$99.70
Purchase #5	$46.97	5.401%	$49.5068	$49.51	$49.50	$49.50
Purchase #6	$118.83	13.184%	$134.4965	$134.50	$134.50	$134.50
Purchase #7	$29.85	7.587%	$32.1147	$32.11	$32.10	$32.10
7 purchase totals =	$594.44		$638.5997	$638.60	$638.60	$638.60