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	$36.70	10.650%	$40.6086	$40.61	$40.60	$40.60
Purchase #2	$217.38	11.862%	$243.1656	$243.17	$243.15	$243.20
Purchase #3	$134.59	5.363%	$141.8081	$141.81	$141.80	$141.80
Purchase #4	$204.94	4.825%	$214.8284	$214.83	$214.85	$214.80
Purchase #5	$121.28	11.241%	$134.9131	$134.91	$134.90	$134.90
Purchase #6	$164.92	12.339%	$185.2695	$185.27	$185.25	$185.30
Purchase #7	$172.72	4.317%	$180.1763	$180.18	$180.20	$180.20
7 purchase totals =	$1,052.53		$1,140.7696	$1,140.78	$1,140.75	$1,140.80