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	$17.90	4.378%	$18.6837	$18.68	$18.70	$18.70
Purchase #2	$187.82	4.493%	$196.2588	$196.26	$196.25	$196.30
Purchase #3	$93.92	12.672%	$105.8215	$105.82	$105.80	$105.80
Purchase #4	$47.55	9.806%	$52.2128	$52.21	$52.20	$52.20
Purchase #5	$62.59	9.103%	$68.2876	$68.29	$68.30	$68.30
Purchase #6	$167.94	10.535%	$185.6325	$185.63	$185.65	$185.60
Purchase #7	$176.48	11.602%	$196.9552	$196.96	$196.95	$197.00
7 purchase totals =	$754.20		$823.8521	$823.85	$823.85	$823.90