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	$234.76	10.520%	$259.4568	$259.46	$259.45	$259.50
Purchase #2	$199.79	12.544%	$224.8517	$224.85	$224.85	$224.90
Purchase #3	$91.57	12.758%	$103.2525	$103.25	$103.25	$103.30
Purchase #4	$5.90	9.377%	$6.4532	$6.45	$6.45	$6.50
Purchase #5	$25.62	11.440%	$28.5509	$28.55	$28.55	$28.60
Purchase #6	$225.90	13.179%	$255.6714	$255.67	$255.65	$255.70
Purchase #7	$220.74	9.359%	$241.3991	$241.40	$241.40	$241.40
7 purchase totals =	$1,004.28		$1,119.6356	$1,119.63	$1,119.60	$1,119.90