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	$231.80	12.752%	$261.3591	$261.36	$261.35	$261.40
Purchase #2	$138.95	8.630%	$150.9414	$150.94	$150.95	$150.90
Purchase #3	$227.60	10.541%	$251.5913	$251.59	$251.60	$251.60
Purchase #4	$133.32	6.160%	$141.5325	$141.53	$141.55	$141.50
Purchase #5	$226.74	10.326%	$250.1532	$250.15	$250.15	$250.20
Purchase #6	$192.34	10.301%	$212.1529	$212.15	$212.15	$212.20
Purchase #7	$137.56	4.351%	$143.5452	$143.55	$143.55	$143.50
7 purchase totals =	$1,288.31		$1,411.2756	$1,411.27	$1,411.30	$1,411.30