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	$131.71	6.403%	$140.1434	$140.14	$140.15	$140.10
Purchase #2	$153.27	7.856%	$165.3109	$165.31	$165.30	$165.30
Purchase #3	$9.84	3.466%	$10.1811	$10.18	$10.20	$10.20
Purchase #4	$71.64	6.687%	$76.4306	$76.43	$76.45	$76.40
Purchase #5	$160.75	3.718%	$166.7267	$166.73	$166.75	$166.70
Purchase #6	$39.87	5.696%	$42.141	$42.14	$42.15	$42.10
Purchase #7	$196.86	10.783%	$218.0874	$218.09	$218.10	$218.10
7 purchase totals =	$763.94		$819.0211	$819.02	$819.10	$818.90