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	$116.76	6.164%	$123.9571	$123.96	$123.95	$124.00
Purchase #2	$66.58	7.347%	$71.4716	$71.47	$71.45	$71.50
Purchase #3	$103.45	12.169%	$116.0388	$116.04	$116.05	$116.00
Purchase #4	$222.61	8.131%	$240.7104	$240.71	$240.70	$240.70
Purchase #5	$127.76	13.676%	$145.2325	$145.23	$145.25	$145.20
Purchase #6	$198.46	5.524%	$209.4229	$209.42	$209.40	$209.40
Purchase #7	$13.81	9.830%	$15.1675	$15.17	$15.15	$15.20
7 purchase totals =	$849.43		$922.0008	$922.00	$921.95	$922.00