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	$138.55	8.571%	$150.4251	$150.43	$150.45	$150.40
Purchase #2	$181.94	13.290%	$206.1198	$206.12	$206.10	$206.10
Purchase #3	$109.82	12.695%	$123.7616	$123.76	$123.75	$123.80
Purchase #4	$162.60	12.259%	$182.5331	$182.53	$182.55	$182.50
Purchase #5	$221.60	9.382%	$242.3905	$242.39	$242.40	$242.40
Purchase #6	$118.55	4.248%	$123.586	$123.59	$123.60	$123.60
Purchase #7	$92.86	7.705%	$100.0149	$100.01	$100.00	$100.00
7 purchase totals =	$1,025.92		$1,128.8310	$1,128.83	$1,128.85	$1,128.80