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	$35.34	11.475%	$39.3953	$39.40	$39.40	$39.40
Purchase #2	$53.97	8.182%	$58.3858	$58.39	$58.40	$58.40
Purchase #3	$124.44	3.198%	$128.4196	$128.42	$128.40	$128.40
Purchase #4	$113.62	3.477%	$117.5706	$117.57	$117.55	$117.60
Purchase #5	$73.87	6.412%	$78.6065	$78.61	$78.60	$78.60
Purchase #6	$133.29	8.324%	$144.3851	$144.39	$144.40	$144.40
Purchase #7	$39.72	6.191%	$42.1791	$42.18	$42.20	$42.20
7 purchase totals =	$574.25		$608.9420	$608.96	$608.95	$609.00