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	$145.49	10.328%	$160.5162	$160.52	$160.50	$160.50
Purchase #2	$31.31	4.843%	$32.8263	$32.83	$32.85	$32.80
Purchase #3	$165.54	13.521%	$187.9227	$187.92	$187.90	$187.90
Purchase #4	$131.31	10.131%	$144.613	$144.61	$144.60	$144.60
Purchase #5	$205.62	8.774%	$223.6611	$223.66	$223.65	$223.70
Purchase #6	$54.45	12.638%	$61.3314	$61.33	$61.35	$61.30
Purchase #7	$151.73	3.433%	$156.9389	$156.94	$156.95	$156.90
7 purchase totals =	$885.45		$967.8096	$967.81	$967.80	$967.70