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	$125.93	10.698%	$139.402	$139.40	$139.40	$139.40
Purchase #2	$102.60	8.495%	$111.3159	$111.32	$111.30	$111.30
Purchase #3	$34.73	10.519%	$38.3832	$38.38	$38.40	$38.40
Purchase #4	$41.51	4.144%	$43.2302	$43.23	$43.25	$43.20
Purchase #5	$54.45	5.790%	$57.6027	$57.60	$57.60	$57.60
Purchase #6	$99.48	13.442%	$112.8521	$112.85	$112.85	$112.90
Purchase #7	$223.31	5.315%	$235.1789	$235.18	$235.20	$235.20
7 purchase totals =	$682.01		$737.9650	$737.96	$738.00	$738.00