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	$143.81	9.285%	$157.1628	$157.16	$157.15	$157.20
Purchase #2	$216.29	3.136%	$223.0729	$223.07	$223.05	$223.10
Purchase #3	$51.35	10.102%	$56.5374	$56.54	$56.55	$56.50
Purchase #4	$228.55	5.840%	$241.8973	$241.90	$241.90	$241.90
Purchase #5	$174.99	5.608%	$184.8034	$184.80	$184.80	$184.80
Purchase #6	$99.94	3.547%	$103.4849	$103.48	$103.50	$103.50
Purchase #7	$98.91	4.569%	$103.4292	$103.43	$103.45	$103.40
7 purchase totals =	$1,013.84		$1,070.3879	$1,070.38	$1,070.40	$1,070.40