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	$138.86	12.436%	$156.1286	$156.13	$156.15	$156.10
Purchase #2	$54.29	12.441%	$61.0442	$61.04	$61.05	$61.00
Purchase #3	$115.28	12.103%	$129.2323	$129.23	$129.25	$129.20
Purchase #4	$82.82	13.837%	$94.2798	$94.28	$94.30	$94.30
Purchase #5	$117.54	4.683%	$123.0444	$123.04	$123.05	$123.00
Purchase #6	$36.47	3.344%	$37.6896	$37.69	$37.70	$37.70
Purchase #7	$240.80	4.102%	$250.6776	$250.68	$250.70	$250.70
7 purchase totals =	$786.06		$852.0965	$852.09	$852.20	$852.00