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	$166.46	7.477%	$178.9062	$178.91	$178.90	$178.90
Purchase #2	$223.87	11.458%	$249.521	$249.52	$249.50	$249.50
Purchase #3	$250.70	13.257%	$283.9353	$283.94	$283.95	$283.90
Purchase #4	$239.87	8.234%	$259.6209	$259.62	$259.60	$259.60
Purchase #5	$83.86	8.175%	$90.7156	$90.72	$90.70	$90.70
Purchase #6	$131.94	9.569%	$144.5653	$144.57	$144.55	$144.60
Purchase #7	$100.65	5.253%	$105.9371	$105.94	$105.95	$105.90
7 purchase totals =	$1,197.35		$1,313.2014	$1,313.22	$1,313.15	$1,313.10