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	$224.81	6.603%	$239.6542	$239.65	$239.65	$239.70
Purchase #2	$86.40	3.143%	$89.1156	$89.12	$89.10	$89.10
Purchase #3	$109.92	12.397%	$123.5468	$123.55	$123.55	$123.50
Purchase #4	$62.93	3.349%	$65.0375	$65.04	$65.05	$65.00
Purchase #5	$220.55	5.852%	$233.4566	$233.46	$233.45	$233.50
Purchase #6	$14.35	13.750%	$16.3231	$16.32	$16.30	$16.30
Purchase #7	$214.37	10.709%	$237.3269	$237.33	$237.35	$237.30
7 purchase totals =	$933.33		$1,004.4607	$1,004.47	$1,004.45	$1,004.40