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	$31.79	3.469%	$32.8928	$32.89	$32.90	$32.90
Purchase #2	$237.74	13.182%	$269.0789	$269.08	$269.10	$269.10
Purchase #3	$67.90	4.479%	$70.9412	$70.94	$70.95	$70.90
Purchase #4	$99.84	12.830%	$112.6495	$112.65	$112.65	$112.60
Purchase #5	$53.37	11.259%	$59.3789	$59.38	$59.40	$59.40
Purchase #6	$153.43	12.419%	$172.4845	$172.48	$172.50	$172.50
Purchase #7	$78.82	11.455%	$87.8488	$87.85	$87.85	$87.80
7 purchase totals =	$722.89		$805.2746	$805.27	$805.35	$805.20