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	$106.31	10.499%	$117.4715	$117.47	$117.45	$117.50
Purchase #2	$34.75	7.257%	$37.2718	$37.27	$37.25	$37.30
Purchase #3	$177.54	10.725%	$196.5812	$196.58	$196.60	$196.60
Purchase #4	$148.72	4.827%	$155.8987	$155.90	$155.90	$155.90
Purchase #5	$117.97	12.491%	$132.7056	$132.71	$132.70	$132.70
Purchase #6	$249.52	9.757%	$273.8657	$273.87	$273.85	$273.90
Purchase #7	$85.85	13.614%	$97.5376	$97.54	$97.55	$97.50
7 purchase totals =	$920.66		$1,011.3321	$1,011.34	$1,011.30	$1,011.40