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	$115.54	4.491%	$120.7289	$120.73	$120.75	$120.70
Purchase #2	$240.86	3.830%	$250.0849	$250.08	$250.10	$250.10
Purchase #3	$41.37	9.256%	$45.1992	$45.20	$45.20	$45.20
Purchase #4	$140.45	9.604%	$153.9388	$153.94	$153.95	$153.90
Purchase #5	$10.28	8.644%	$11.1686	$11.17	$11.15	$11.20
Purchase #6	$239.57	6.828%	$255.9278	$255.93	$255.95	$255.90
Purchase #7	$170.75	5.149%	$179.5419	$179.54	$179.55	$179.50
7 purchase totals =	$958.82		$1,016.5901	$1,016.59	$1,016.65	$1,016.50