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	$89.44	12.592%	$100.7023	$100.70	$100.70	$100.70
Purchase #2	$200.63	10.572%	$221.8406	$221.84	$221.85	$221.80
Purchase #3	$75.69	3.632%	$78.4391	$78.44	$78.45	$78.40
Purchase #4	$14.52	9.287%	$15.8685	$15.87	$15.85	$15.90
Purchase #5	$42.54	12.327%	$47.7839	$47.78	$47.80	$47.80
Purchase #6	$10.53	9.707%	$11.5521	$11.55	$11.55	$11.60
Purchase #7	$72.72	11.678%	$81.2122	$81.21	$81.20	$81.20
7 purchase totals =	$506.07		$557.3987	$557.39	$557.40	$557.40