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	$40.40	4.688%	$42.294	$42.29	$42.30	$42.30
Purchase #2	$38.39	13.507%	$43.5753	$43.58	$43.60	$43.60
Purchase #3	$16.86	3.871%	$17.5127	$17.51	$17.50	$17.50
Purchase #4	$60.53	11.268%	$67.3505	$67.35	$67.35	$67.40
Purchase #5	$235.28	13.442%	$266.9063	$266.91	$266.90	$266.90
Purchase #6	$71.44	12.418%	$80.3114	$80.31	$80.30	$80.30
Purchase #7	$157.34	13.258%	$178.2001	$178.20	$178.20	$178.20
7 purchase totals =	$620.24		$696.1503	$696.15	$696.15	$696.20