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	$22.53	10.342%	$24.8601	$24.86	$24.85	$24.90
Purchase #2	$41.58	6.742%	$44.3833	$44.38	$44.40	$44.40
Purchase #3	$32.75	11.801%	$36.6148	$36.61	$36.60	$36.60
Purchase #4	$227.76	12.216%	$255.5832	$255.58	$255.60	$255.60
Purchase #5	$206.80	13.359%	$234.4264	$234.43	$234.45	$234.40
Purchase #6	$152.74	4.670%	$159.873	$159.87	$159.85	$159.90
Purchase #7	$228.80	5.716%	$241.8782	$241.88	$241.90	$241.90
7 purchase totals =	$912.96		$997.6190	$997.61	$997.65	$997.70