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	$5.81	7.284%	$6.2332	$6.23	$6.25	$6.20
Purchase #2	$219.35	10.143%	$241.5987	$241.60	$241.60	$241.60
Purchase #3	$25.75	6.850%	$27.5139	$27.51	$27.50	$27.50
Purchase #4	$37.53	12.343%	$42.1623	$42.16	$42.15	$42.20
Purchase #5	$40.30	3.318%	$41.6372	$41.64	$41.65	$41.60
Purchase #6	$56.53	5.239%	$59.4916	$59.49	$59.50	$59.50
Purchase #7	$248.32	5.133%	$261.0663	$261.07	$261.05	$261.10
7 purchase totals =	$633.59		$679.7032	$679.70	$679.70	$679.70