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	$139.43	13.693%	$158.5221	$158.52	$158.50	$158.50
Purchase #2	$41.35	4.218%	$43.0941	$43.09	$43.10	$43.10
Purchase #3	$180.46	9.280%	$197.2067	$197.21	$197.20	$197.20
Purchase #4	$63.59	13.779%	$72.3521	$72.35	$72.35	$72.40
Purchase #5	$237.46	12.645%	$267.4868	$267.49	$267.50	$267.50
Purchase #6	$133.78	8.465%	$145.1045	$145.10	$145.10	$145.10
Purchase #7	$135.36	6.666%	$144.3831	$144.38	$144.40	$144.40
7 purchase totals =	$931.43		$1,028.1494	$1,028.14	$1,028.15	$1,028.20