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	$40.81	4.248%	$42.5436	$42.54	$42.55	$42.50
Purchase #2	$81.88	9.256%	$89.4588	$89.46	$89.45	$89.50
Purchase #3	$124.83	10.833%	$138.3528	$138.35	$138.35	$138.40
Purchase #4	$15.43	7.522%	$16.5906	$16.59	$16.60	$16.60
Purchase #5	$116.30	11.529%	$129.7082	$129.71	$129.70	$129.70
Purchase #6	$21.88	13.408%	$24.8137	$24.81	$24.80	$24.80
Purchase #7	$64.89	3.232%	$66.9872	$66.99	$67.00	$67.00
7 purchase totals =	$466.02		$508.4549	$508.45	$508.45	$508.50