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	$104.83	6.394%	$111.5328	$111.53	$111.55	$111.50
Purchase #2	$160.53	10.431%	$177.2749	$177.27	$177.25	$177.30
Purchase #3	$171.47	13.187%	$194.0817	$194.08	$194.10	$194.10
Purchase #4	$53.46	5.352%	$56.3212	$56.32	$56.30	$56.30
Purchase #5	$49.96	7.515%	$53.7145	$53.71	$53.70	$53.70
Purchase #6	$172.59	8.504%	$187.2671	$187.27	$187.25	$187.30
Purchase #7	$57.39	11.680%	$64.0932	$64.09	$64.10	$64.10
7 purchase totals =	$770.23		$844.2854	$844.27	$844.25	$844.30