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	$80.88	3.278%	$83.5312	$83.53	$83.55	$83.50
Purchase #2	$93.61	5.602%	$98.854	$98.85	$98.85	$98.90
Purchase #3	$122.70	4.191%	$127.8424	$127.84	$127.85	$127.80
Purchase #4	$66.36	6.543%	$70.7019	$70.70	$70.70	$70.70
Purchase #5	$29.88	7.207%	$32.0335	$32.03	$32.05	$32.00
Purchase #6	$146.46	12.369%	$164.5756	$164.58	$164.60	$164.60
Purchase #7	$225.28	13.418%	$255.5081	$255.51	$255.50	$255.50
7 purchase totals =	$765.17		$833.0467	$833.04	$833.10	$833.00