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	$80.36	11.371%	$89.4977	$89.50	$89.50	$89.50
Purchase #2	$102.67	8.602%	$111.5017	$111.50	$111.50	$111.50
Purchase #3	$138.29	7.156%	$148.186	$148.19	$148.20	$148.20
Purchase #4	$248.50	12.465%	$279.4755	$279.48	$279.50	$279.50
Purchase #5	$111.58	8.254%	$120.7898	$120.79	$120.80	$120.80
Purchase #6	$238.57	13.558%	$270.9153	$270.92	$270.90	$270.90
Purchase #7	$49.42	13.548%	$56.1154	$56.12	$56.10	$56.10
7 purchase totals =	$969.39		$1,076.4814	$1,076.50	$1,076.50	$1,076.50