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	$11.78	3.367%	$12.1766	$12.18	$12.20	$12.20
Purchase #2	$248.32	12.698%	$279.8517	$279.85	$279.85	$279.90
Purchase #3	$241.81	5.706%	$255.6077	$255.61	$255.60	$255.60
Purchase #4	$196.90	8.379%	$213.3983	$213.40	$213.40	$213.40
Purchase #5	$58.74	10.340%	$64.8137	$64.81	$64.80	$64.80
Purchase #6	$200.81	12.418%	$225.7466	$225.75	$225.75	$225.70
Purchase #7	$29.77	6.756%	$31.7813	$31.78	$31.80	$31.80
7 purchase totals =	$988.13		$1,083.3759	$1,083.38	$1,083.40	$1,083.40