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	$87.47	13.796%	$99.5374	$99.54	$99.55	$99.50
Purchase #2	$115.68	13.262%	$131.0215	$131.02	$131.00	$131.00
Purchase #3	$90.70	12.470%	$102.0103	$102.01	$102.00	$102.00
Purchase #4	$17.61	9.515%	$19.2856	$19.29	$19.30	$19.30
Purchase #5	$111.57	4.353%	$116.4266	$116.43	$116.45	$116.40
Purchase #6	$105.68	7.762%	$113.8829	$113.88	$113.90	$113.90
Purchase #7	$44.85	13.739%	$51.0119	$51.01	$51.00	$51.00
7 purchase totals =	$573.56		$633.1762	$633.18	$633.20	$633.10