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	$231.70	12.842%	$261.4549	$261.45	$261.45	$261.50
Purchase #2	$54.51	13.460%	$61.847	$61.85	$61.85	$61.80
Purchase #3	$37.60	7.658%	$40.4794	$40.48	$40.50	$40.50
Purchase #4	$121.74	5.837%	$128.846	$128.85	$128.85	$128.80
Purchase #5	$162.53	8.811%	$176.8505	$176.85	$176.85	$176.90
Purchase #6	$77.52	3.230%	$80.0239	$80.02	$80.00	$80.00
Purchase #7	$155.30	10.115%	$171.0086	$171.01	$171.00	$171.00
7 purchase totals =	$840.90		$920.5103	$920.51	$920.50	$920.50