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	$83.33	8.577%	$90.4772	$90.48	$90.50	$90.50
Purchase #2	$140.87	12.673%	$158.7225	$158.72	$158.70	$158.70
Purchase #3	$135.92	8.810%	$147.8946	$147.89	$147.90	$147.90
Purchase #4	$175.94	12.291%	$197.5648	$197.56	$197.55	$197.60
Purchase #5	$71.68	13.805%	$81.5754	$81.58	$81.60	$81.60
Purchase #6	$42.35	8.476%	$45.9396	$45.94	$45.95	$45.90
Purchase #7	$94.60	11.690%	$105.6587	$105.66	$105.65	$105.70
7 purchase totals =	$744.69		$827.8328	$827.83	$827.85	$827.90