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	$104.55	12.462%	$117.579	$117.58	$117.60	$117.60
Purchase #2	$185.82	9.518%	$203.5063	$203.51	$203.50	$203.50
Purchase #3	$42.81	5.224%	$45.0464	$45.05	$45.05	$45.00
Purchase #4	$59.89	6.528%	$63.7996	$63.80	$63.80	$63.80
Purchase #5	$23.31	3.664%	$24.1641	$24.16	$24.15	$24.20
Purchase #6	$114.85	3.456%	$118.8192	$118.82	$118.80	$118.80
Purchase #7	$95.82	8.425%	$103.8928	$103.89	$103.90	$103.90
7 purchase totals =	$627.05		$676.8074	$676.81	$676.80	$676.80