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	$16.38	9.221%	$17.8904	$17.89	$17.90	$17.90
Purchase #2	$142.58	5.770%	$150.8069	$150.81	$150.80	$150.80
Purchase #3	$224.88	6.844%	$240.2708	$240.27	$240.25	$240.30
Purchase #4	$37.96	11.677%	$42.3926	$42.39	$42.40	$42.40
Purchase #5	$136.51	12.396%	$153.4318	$153.43	$153.45	$153.40
Purchase #6	$36.54	11.247%	$40.6497	$40.65	$40.65	$40.60
Purchase #7	$102.57	11.288%	$114.1481	$114.15	$114.15	$114.10
7 purchase totals =	$697.42		$759.5903	$759.59	$759.60	$759.50