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	$35.66	7.659%	$38.3912	$38.39	$38.40	$38.40
Purchase #2	$219.41	12.325%	$246.4523	$246.45	$246.45	$246.50
Purchase #3	$106.75	11.512%	$119.0391	$119.04	$119.05	$119.00
Purchase #4	$36.73	9.493%	$40.2168	$40.22	$40.20	$40.20
Purchase #5	$130.97	8.824%	$142.5268	$142.53	$142.55	$142.50
Purchase #6	$225.46	11.239%	$250.7994	$250.80	$250.80	$250.80
Purchase #7	$127.93	10.344%	$141.1631	$141.16	$141.15	$141.20
7 purchase totals =	$882.91		$978.5887	$978.59	$978.60	$978.60