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	$99.29	6.232%	$105.4778	$105.48	$105.50	$105.50
Purchase #2	$31.53	13.768%	$35.8711	$35.87	$35.85	$35.90
Purchase #3	$230.66	8.215%	$249.6087	$249.61	$249.60	$249.60
Purchase #4	$46.29	8.852%	$50.3876	$50.39	$50.40	$50.40
Purchase #5	$13.78	3.273%	$14.231	$14.23	$14.25	$14.20
Purchase #6	$161.29	13.676%	$183.348	$183.35	$183.35	$183.30
Purchase #7	$34.31	11.383%	$38.2155	$38.22	$38.20	$38.20
7 purchase totals =	$617.15		$677.1397	$677.15	$677.15	$677.10