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	$113.60	9.546%	$124.4443	$124.44	$124.45	$124.40
Purchase #2	$207.62	7.130%	$222.4233	$222.42	$222.40	$222.40
Purchase #3	$249.96	3.860%	$259.6085	$259.61	$259.60	$259.60
Purchase #4	$172.40	4.527%	$180.2045	$180.20	$180.20	$180.20
Purchase #5	$68.77	5.687%	$72.6809	$72.68	$72.70	$72.70
Purchase #6	$94.44	6.155%	$100.2528	$100.25	$100.25	$100.30
Purchase #7	$30.82	11.360%	$34.3212	$34.32	$34.30	$34.30
7 purchase totals =	$937.61		$993.9355	$993.92	$993.90	$993.90