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	$240.28	8.871%	$261.5952	$261.60	$261.60	$261.60
Purchase #2	$54.43	6.329%	$57.8749	$57.87	$57.85	$57.90
Purchase #3	$130.42	10.350%	$143.9185	$143.92	$143.90	$143.90
Purchase #4	$121.66	9.780%	$133.5583	$133.56	$133.55	$133.60
Purchase #5	$111.69	8.534%	$121.2216	$121.22	$121.20	$121.20
Purchase #6	$38.40	5.745%	$40.6061	$40.61	$40.60	$40.60
Purchase #7	$63.94	13.592%	$72.6307	$72.63	$72.65	$72.60
7 purchase totals =	$760.82		$831.4053	$831.41	$831.35	$831.40