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	$9.97	12.572%	$11.2234	$11.22	$11.20	$11.20
Purchase #2	$92.35	10.561%	$102.1031	$102.10	$102.10	$102.10
Purchase #3	$185.58	3.409%	$191.9064	$191.91	$191.90	$191.90
Purchase #4	$167.86	11.759%	$187.5987	$187.60	$187.60	$187.60
Purchase #5	$96.44	4.148%	$100.4403	$100.44	$100.45	$100.40
Purchase #6	$156.56	3.410%	$161.8987	$161.90	$161.90	$161.90
Purchase #7	$139.71	7.726%	$150.504	$150.50	$150.50	$150.50
7 purchase totals =	$848.47		$905.6746	$905.67	$905.65	$905.60