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	$102.70	13.808%	$116.8808	$116.88	$116.90	$116.90
Purchase #2	$129.61	7.436%	$139.2478	$139.25	$139.25	$139.20
Purchase #3	$48.44	9.468%	$53.0263	$53.03	$53.05	$53.00
Purchase #4	$160.99	4.833%	$168.7706	$168.77	$168.75	$168.80
Purchase #5	$243.45	8.385%	$263.8633	$263.86	$263.85	$263.90
Purchase #6	$11.34	6.187%	$12.0416	$12.04	$12.05	$12.00
Purchase #7	$131.72	4.536%	$137.6948	$137.69	$137.70	$137.70
7 purchase totals =	$828.25		$891.5252	$891.52	$891.55	$891.50