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	$12.54	5.825%	$13.2705	$13.27	$13.25	$13.30
Purchase #2	$231.91	3.139%	$239.1897	$239.19	$239.20	$239.20
Purchase #3	$56.77	13.764%	$64.5838	$64.58	$64.60	$64.60
Purchase #4	$141.95	11.525%	$158.3097	$158.31	$158.30	$158.30
Purchase #5	$118.34	11.336%	$131.755	$131.76	$131.75	$131.80
Purchase #6	$208.32	4.839%	$218.4006	$218.40	$218.40	$218.40
Purchase #7	$246.28	6.168%	$261.4706	$261.47	$261.45	$261.50
7 purchase totals =	$1,016.11		$1,086.9799	$1,086.98	$1,086.95	$1,087.10