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	$243.59	7.242%	$261.2308	$261.23	$261.25	$261.20
Purchase #2	$155.92	3.169%	$160.8611	$160.86	$160.85	$160.90
Purchase #3	$119.76	10.718%	$132.5959	$132.60	$132.60	$132.60
Purchase #4	$107.64	10.586%	$119.0348	$119.03	$119.05	$119.00
Purchase #5	$150.34	8.225%	$162.7055	$162.71	$162.70	$162.70
Purchase #6	$27.82	12.411%	$31.2727	$31.27	$31.25	$31.30
Purchase #7	$110.82	4.574%	$115.8889	$115.89	$115.90	$115.90
7 purchase totals =	$915.89		$983.5897	$983.59	$983.60	$983.60