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	$123.70	7.399%	$132.8526	$132.85	$132.85	$132.90
Purchase #2	$248.75	10.473%	$274.8016	$274.80	$274.80	$274.80
Purchase #3	$83.65	6.796%	$89.3349	$89.33	$89.35	$89.30
Purchase #4	$138.37	8.582%	$150.2449	$150.24	$150.25	$150.20
Purchase #5	$53.95	12.328%	$60.601	$60.60	$60.60	$60.60
Purchase #6	$24.85	12.105%	$27.8581	$27.86	$27.85	$27.90
Purchase #7	$115.31	9.826%	$126.6404	$126.64	$126.65	$126.60
7 purchase totals =	$788.58		$862.3335	$862.32	$862.35	$862.30