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	$230.95	12.774%	$260.4516	$260.45	$260.45	$260.50
Purchase #2	$191.25	10.491%	$211.314	$211.31	$211.30	$211.30
Purchase #3	$165.54	3.632%	$171.5524	$171.55	$171.55	$171.60
Purchase #4	$86.53	7.136%	$92.7048	$92.70	$92.70	$92.70
Purchase #5	$92.84	13.199%	$105.094	$105.09	$105.10	$105.10
Purchase #6	$111.42	5.186%	$117.1982	$117.20	$117.20	$117.20
Purchase #7	$37.82	8.188%	$40.9167	$40.92	$40.90	$40.90
7 purchase totals =	$916.35		$999.2317	$999.22	$999.20	$999.30