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	$243.97	5.691%	$257.8543	$257.85	$257.85	$257.90
Purchase #2	$180.88	8.840%	$196.8698	$196.87	$196.85	$196.90
Purchase #3	$35.47	6.624%	$37.8195	$37.82	$37.80	$37.80
Purchase #4	$203.71	12.186%	$228.5341	$228.53	$228.55	$228.50
Purchase #5	$132.92	7.257%	$142.566	$142.57	$142.55	$142.60
Purchase #6	$134.36	12.538%	$151.2061	$151.21	$151.20	$151.20
Purchase #7	$46.60	8.581%	$50.5987	$50.60	$50.60	$50.60
7 purchase totals =	$977.91		$1,065.4485	$1,065.45	$1,065.40	$1,065.50