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	$54.85	3.570%	$56.8081	$56.81	$56.80	$56.80
Purchase #2	$184.80	6.161%	$196.1855	$196.19	$196.20	$196.20
Purchase #3	$116.46	5.475%	$122.8362	$122.84	$122.85	$122.80
Purchase #4	$138.35	10.111%	$152.3386	$152.34	$152.35	$152.30
Purchase #5	$92.98	7.336%	$99.801	$99.80	$99.80	$99.80
Purchase #6	$102.90	13.358%	$116.6454	$116.65	$116.65	$116.60
Purchase #7	$117.57	7.120%	$125.941	$125.94	$125.95	$125.90
7 purchase totals =	$807.91		$870.5558	$870.57	$870.60	$870.40