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	$71.60	5.443%	$75.4972	$75.50	$75.50	$75.50
Purchase #2	$158.71	6.569%	$169.1357	$169.14	$169.15	$169.10
Purchase #3	$39.40	6.780%	$42.0713	$42.07	$42.05	$42.10
Purchase #4	$74.36	7.601%	$80.0121	$80.01	$80.00	$80.00
Purchase #5	$108.71	8.383%	$117.8232	$117.82	$117.80	$117.80
Purchase #6	$34.96	11.402%	$38.9461	$38.95	$38.95	$38.90
Purchase #7	$129.86	7.373%	$139.4346	$139.43	$139.45	$139.40
7 purchase totals =	$617.60		$662.9202	$662.92	$662.90	$662.80