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	$38.87	13.561%	$44.1412	$44.14	$44.15	$44.10
Purchase #2	$188.47	9.628%	$206.6159	$206.62	$206.60	$206.60
Purchase #3	$80.78	3.628%	$83.7107	$83.71	$83.70	$83.70
Purchase #4	$177.31	10.605%	$196.1137	$196.11	$196.10	$196.10
Purchase #5	$39.60	6.484%	$42.1677	$42.17	$42.15	$42.20
Purchase #6	$155.42	4.292%	$162.0906	$162.09	$162.10	$162.10
Purchase #7	$61.94	3.577%	$64.1556	$64.16	$64.15	$64.20
7 purchase totals =	$742.39		$798.9954	$799.00	$798.95	$799.00