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	$38.51	6.229%	$40.9088	$40.91	$40.90	$40.90
Purchase #2	$41.85	7.703%	$45.0737	$45.07	$45.05	$45.10
Purchase #3	$43.55	11.462%	$48.5417	$48.54	$48.55	$48.50
Purchase #4	$207.65	11.531%	$231.5941	$231.59	$231.60	$231.60
Purchase #5	$40.44	11.760%	$45.1957	$45.20	$45.20	$45.20
Purchase #6	$241.25	11.116%	$268.0674	$268.07	$268.05	$268.10
Purchase #7	$90.44	7.671%	$97.3777	$97.38	$97.40	$97.40
7 purchase totals =	$703.69		$776.7591	$776.76	$776.75	$776.80