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	$145.64	13.266%	$164.9606	$164.96	$164.95	$165.00
Purchase #2	$151.49	10.120%	$166.8208	$166.82	$166.80	$166.80
Purchase #3	$52.46	12.635%	$59.0883	$59.09	$59.10	$59.10
Purchase #4	$85.85	4.413%	$89.6386	$89.64	$89.65	$89.60
Purchase #5	$23.44	13.872%	$26.6916	$26.69	$26.70	$26.70
Purchase #6	$81.62	10.542%	$90.2244	$90.22	$90.20	$90.20
Purchase #7	$66.31	7.321%	$71.1646	$71.16	$71.15	$71.20
7 purchase totals =	$606.81		$668.5889	$668.58	$668.55	$668.60