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	$246.83	11.633%	$275.5437	$275.54	$275.55	$275.50
Purchase #2	$38.63	13.422%	$43.8149	$43.81	$43.80	$43.80
Purchase #3	$206.67	10.815%	$229.0214	$229.02	$229.00	$229.00
Purchase #4	$202.72	8.299%	$219.5437	$219.54	$219.55	$219.50
Purchase #5	$35.63	7.547%	$38.319	$38.32	$38.30	$38.30
Purchase #6	$67.60	4.617%	$70.7211	$70.72	$70.70	$70.70
Purchase #7	$23.46	4.432%	$24.4997	$24.50	$24.50	$24.50
7 purchase totals =	$821.54		$901.4635	$901.45	$901.40	$901.30