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	$236.78	13.823%	$269.5101	$269.51	$269.50	$269.50
Purchase #2	$100.31	9.184%	$109.5225	$109.52	$109.50	$109.50
Purchase #3	$235.32	5.395%	$248.0155	$248.02	$248.00	$248.00
Purchase #4	$205.86	4.162%	$214.4279	$214.43	$214.45	$214.40
Purchase #5	$99.60	4.204%	$103.7872	$103.79	$103.80	$103.80
Purchase #6	$54.88	8.506%	$59.5481	$59.55	$59.55	$59.50
Purchase #7	$198.93	9.731%	$218.2879	$218.29	$218.30	$218.30
7 purchase totals =	$1,131.68		$1,223.0992	$1,223.11	$1,223.10	$1,223.00