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	$27.27	4.467%	$28.4882	$28.49	$28.50	$28.50
Purchase #2	$40.99	5.613%	$43.2908	$43.29	$43.30	$43.30
Purchase #3	$60.68	3.471%	$62.7862	$62.79	$62.80	$62.80
Purchase #4	$146.58	8.419%	$158.9206	$158.92	$158.90	$158.90
Purchase #5	$148.32	12.357%	$166.6479	$166.65	$166.65	$166.60
Purchase #6	$16.75	9.507%	$18.3424	$18.34	$18.35	$18.30
Purchase #7	$17.77	10.265%	$19.5941	$19.59	$19.60	$19.60
7 purchase totals =	$458.36		$498.0702	$498.07	$498.10	$498.00