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	$109.62	8.727%	$119.1865	$119.19	$119.20	$119.20
Purchase #2	$141.25	6.385%	$150.2688	$150.27	$150.25	$150.30
Purchase #3	$31.65	11.335%	$35.2375	$35.24	$35.25	$35.20
Purchase #4	$32.49	13.571%	$36.8992	$36.90	$36.90	$36.90
Purchase #5	$19.90	7.389%	$21.3704	$21.37	$21.35	$21.40
Purchase #6	$176.73	12.311%	$198.4872	$198.49	$198.50	$198.50
Purchase #7	$31.86	11.680%	$35.5812	$35.58	$35.60	$35.60
7 purchase totals =	$543.50		$597.0308	$597.04	$597.05	$597.10