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	$36.79	7.273%	$39.4657	$39.47	$39.45	$39.50
Purchase #2	$80.41	10.504%	$88.8563	$88.86	$88.85	$88.90
Purchase #3	$77.66	6.218%	$82.4889	$82.49	$82.50	$82.50
Purchase #4	$155.27	12.850%	$175.2222	$175.22	$175.20	$175.20
Purchase #5	$140.43	5.595%	$148.2871	$148.29	$148.30	$148.30
Purchase #6	$134.87	13.730%	$153.3877	$153.39	$153.40	$153.40
Purchase #7	$67.78	13.683%	$77.0543	$77.05	$77.05	$77.10
7 purchase totals =	$693.21		$764.7622	$764.77	$764.75	$764.90