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	$54.36	7.590%	$58.4859	$58.49	$58.50	$58.50
Purchase #2	$236.64	5.162%	$248.8554	$248.86	$248.85	$248.90
Purchase #3	$126.77	3.562%	$131.2855	$131.29	$131.30	$131.30
Purchase #4	$178.45	4.383%	$186.2715	$186.27	$186.25	$186.30
Purchase #5	$81.60	11.288%	$90.811	$90.81	$90.80	$90.80
Purchase #6	$48.57	9.242%	$53.0588	$53.06	$53.05	$53.10
Purchase #7	$198.92	4.341%	$207.5551	$207.56	$207.55	$207.60
7 purchase totals =	$925.31		$976.3232	$976.34	$976.30	$976.50