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	$23.90	3.798%	$24.8077	$24.81	$24.80	$24.80
Purchase #2	$14.37	7.256%	$15.4127	$15.41	$15.40	$15.40
Purchase #3	$170.32	5.397%	$179.5122	$179.51	$179.50	$179.50
Purchase #4	$209.70	6.482%	$223.2928	$223.29	$223.30	$223.30
Purchase #5	$51.29	7.594%	$55.185	$55.19	$55.20	$55.20
Purchase #6	$95.67	13.530%	$108.6142	$108.61	$108.60	$108.60
Purchase #7	$37.66	13.856%	$42.8782	$42.88	$42.90	$42.90
7 purchase totals =	$602.91		$649.7028	$649.70	$649.70	$649.70