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	$64.73	12.432%	$72.7772	$72.78	$72.80	$72.80
Purchase #2	$225.32	13.253%	$255.1817	$255.18	$255.20	$255.20
Purchase #3	$106.77	12.782%	$120.4173	$120.42	$120.40	$120.40
Purchase #4	$93.71	3.604%	$97.0873	$97.09	$97.10	$97.10
Purchase #5	$37.59	3.286%	$38.8252	$38.83	$38.85	$38.80
Purchase #6	$183.94	12.132%	$206.2556	$206.26	$206.25	$206.30
Purchase #7	$170.65	5.404%	$179.8719	$179.87	$179.85	$179.90
7 purchase totals =	$882.71		$970.4162	$970.43	$970.45	$970.50