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	$12.50	3.375%	$12.9219	$12.92	$12.90	$12.90
Purchase #2	$101.86	13.476%	$115.5867	$115.59	$115.60	$115.60
Purchase #3	$82.81	4.763%	$86.7542	$86.75	$86.75	$86.80
Purchase #4	$250.69	5.828%	$265.3002	$265.30	$265.30	$265.30
Purchase #5	$13.81	7.258%	$14.8123	$14.81	$14.80	$14.80
Purchase #6	$40.39	12.751%	$45.5401	$45.54	$45.55	$45.50
Purchase #7	$250.30	11.773%	$279.7678	$279.77	$279.75	$279.80
7 purchase totals =	$752.36		$820.6832	$820.68	$820.65	$820.70