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	$17.30	9.182%	$18.8885	$18.89	$18.90	$18.90
Purchase #2	$20.80	13.663%	$23.6419	$23.64	$23.65	$23.60
Purchase #3	$95.83	6.839%	$102.3838	$102.38	$102.40	$102.40
Purchase #4	$19.69	7.472%	$21.1612	$21.16	$21.15	$21.20
Purchase #5	$40.98	9.711%	$44.9596	$44.96	$44.95	$45.00
Purchase #6	$108.51	7.726%	$116.8935	$116.89	$116.90	$116.90
Purchase #7	$53.37	4.224%	$55.6243	$55.62	$55.60	$55.60
7 purchase totals =	$356.48		$383.5528	$383.54	$383.55	$383.60