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	$14.39	6.610%	$15.3412	$15.34	$15.35	$15.30
Purchase #2	$209.72	10.405%	$231.5414	$231.54	$231.55	$231.50
Purchase #3	$168.77	8.119%	$182.4724	$182.47	$182.45	$182.50
Purchase #4	$213.46	10.219%	$235.2735	$235.27	$235.25	$235.30
Purchase #5	$250.87	11.463%	$279.6272	$279.63	$279.65	$279.60
Purchase #6	$115.29	10.232%	$127.0865	$127.09	$127.10	$127.10
Purchase #7	$213.70	5.518%	$225.492	$225.49	$225.50	$225.50
7 purchase totals =	$1,186.20		$1,296.8342	$1,296.83	$1,296.85	$1,296.80