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	$17.33	8.322%	$18.7722	$18.77	$18.75	$18.80
Purchase #2	$114.44	4.479%	$119.5658	$119.57	$119.55	$119.60
Purchase #3	$160.66	8.860%	$174.8945	$174.89	$174.90	$174.90
Purchase #4	$13.92	11.408%	$15.508	$15.51	$15.50	$15.50
Purchase #5	$16.64	12.503%	$18.7205	$18.72	$18.70	$18.70
Purchase #6	$40.51	4.325%	$42.2621	$42.26	$42.25	$42.30
Purchase #7	$102.90	5.382%	$108.4381	$108.44	$108.45	$108.40
7 purchase totals =	$466.40		$498.1612	$498.16	$498.10	$498.20