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	$80.37	6.357%	$85.4791	$85.48	$85.50	$85.50
Purchase #2	$139.68	11.231%	$155.3675	$155.37	$155.35	$155.40
Purchase #3	$181.64	3.807%	$188.555	$188.56	$188.55	$188.60
Purchase #4	$236.86	6.760%	$252.8717	$252.87	$252.85	$252.90
Purchase #5	$21.55	11.609%	$24.0517	$24.05	$24.05	$24.10
Purchase #6	$38.67	9.389%	$42.3007	$42.30	$42.30	$42.30
Purchase #7	$134.30	6.682%	$143.2739	$143.27	$143.25	$143.30
7 purchase totals =	$833.07		$891.8996	$891.90	$891.85	$892.10