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	$42.86	13.270%	$48.5475	$48.55	$48.55	$48.50
Purchase #2	$238.96	8.604%	$259.5201	$259.52	$259.50	$259.50
Purchase #3	$132.56	3.789%	$137.5827	$137.58	$137.60	$137.60
Purchase #4	$36.42	12.254%	$40.8829	$40.88	$40.90	$40.90
Purchase #5	$85.39	4.423%	$89.1668	$89.17	$89.15	$89.20
Purchase #6	$58.90	5.734%	$62.2773	$62.28	$62.30	$62.30
Purchase #7	$187.39	9.358%	$204.926	$204.93	$204.95	$204.90
7 purchase totals =	$782.48		$842.9033	$842.91	$842.95	$842.90