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	$25.79	6.479%	$27.4609	$27.46	$27.45	$27.50
Purchase #2	$103.81	7.368%	$111.4587	$111.46	$111.45	$111.50
Purchase #3	$39.42	5.341%	$41.5254	$41.53	$41.55	$41.50
Purchase #4	$37.55	4.402%	$39.203	$39.20	$39.20	$39.20
Purchase #5	$14.68	10.560%	$16.2302	$16.23	$16.25	$16.20
Purchase #6	$134.45	13.340%	$152.3856	$152.39	$152.40	$152.40
Purchase #7	$146.30	5.613%	$154.5118	$154.51	$154.50	$154.50
7 purchase totals =	$502.00		$542.7756	$542.78	$542.80	$542.80