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	$241.66	13.615%	$274.562	$274.56	$274.55	$274.60
Purchase #2	$200.29	3.863%	$208.0272	$208.03	$208.05	$208.00
Purchase #3	$35.26	11.746%	$39.4016	$39.40	$39.40	$39.40
Purchase #4	$82.60	9.398%	$90.3627	$90.36	$90.35	$90.40
Purchase #5	$27.81	13.303%	$31.5096	$31.51	$31.50	$31.50
Purchase #6	$33.68	3.682%	$34.9201	$34.92	$34.90	$34.90
Purchase #7	$123.80	12.787%	$139.6303	$139.63	$139.65	$139.60
7 purchase totals =	$745.10		$818.4135	$818.41	$818.40	$818.40