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	$132.40	7.189%	$141.9182	$141.92	$141.90	$141.90
Purchase #2	$139.55	9.833%	$153.272	$153.27	$153.25	$153.30
Purchase #3	$245.72	13.553%	$279.0224	$279.02	$279.00	$279.00
Purchase #4	$166.29	10.845%	$184.3242	$184.32	$184.30	$184.30
Purchase #5	$163.70	11.560%	$182.6237	$182.62	$182.60	$182.60
Purchase #6	$12.60	6.139%	$13.3735	$13.37	$13.35	$13.40
Purchase #7	$148.81	13.449%	$168.8235	$168.82	$168.80	$168.80
7 purchase totals =	$1,009.07		$1,123.3575	$1,123.34	$1,123.20	$1,123.30