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	$78.72	5.206%	$82.8182	$82.82	$82.80	$82.80
Purchase #2	$47.59	9.525%	$52.1229	$52.12	$52.10	$52.10
Purchase #3	$250.37	13.618%	$284.4654	$284.47	$284.45	$284.50
Purchase #4	$86.87	9.759%	$95.3476	$95.35	$95.35	$95.30
Purchase #5	$83.80	4.512%	$87.5811	$87.58	$87.60	$87.60
Purchase #6	$230.29	13.847%	$262.1783	$262.18	$262.20	$262.20
Purchase #7	$102.43	9.174%	$111.8269	$111.83	$111.85	$111.80
7 purchase totals =	$880.07		$976.3404	$976.35	$976.35	$976.30