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	$16.30	7.123%	$17.461	$17.46	$17.45	$17.50
Purchase #2	$48.76	13.815%	$55.4962	$55.50	$55.50	$55.50
Purchase #3	$67.47	6.540%	$71.8825	$71.88	$71.90	$71.90
Purchase #4	$42.30	9.183%	$46.1844	$46.18	$46.20	$46.20
Purchase #5	$139.69	11.224%	$155.3688	$155.37	$155.35	$155.40
Purchase #6	$203.51	10.859%	$225.6092	$225.61	$225.60	$225.60
Purchase #7	$136.53	13.444%	$154.8851	$154.89	$154.90	$154.90
7 purchase totals =	$654.56		$726.8872	$726.89	$726.90	$727.00