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	$73.48	5.268%	$77.3509	$77.35	$77.35	$77.40
Purchase #2	$223.87	9.255%	$244.5892	$244.59	$244.60	$244.60
Purchase #3	$93.83	7.594%	$100.9555	$100.96	$100.95	$101.00
Purchase #4	$12.46	13.441%	$14.1347	$14.13	$14.15	$14.10
Purchase #5	$246.29	8.212%	$266.5153	$266.52	$266.50	$266.50
Purchase #6	$89.93	11.478%	$100.2522	$100.25	$100.25	$100.30
Purchase #7	$21.85	13.482%	$24.7958	$24.80	$24.80	$24.80
7 purchase totals =	$761.71		$828.5936	$828.60	$828.60	$828.70