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	$131.92	7.272%	$141.5132	$141.51	$141.50	$141.50
Purchase #2	$246.30	13.506%	$279.5653	$279.57	$279.55	$279.60
Purchase #3	$112.80	4.700%	$118.1016	$118.10	$118.10	$118.10
Purchase #4	$129.79	7.496%	$139.5191	$139.52	$139.50	$139.50
Purchase #5	$229.74	5.162%	$241.5992	$241.60	$241.60	$241.60
Purchase #6	$139.60	3.227%	$144.1049	$144.10	$144.10	$144.10
Purchase #7	$119.25	6.393%	$126.8737	$126.87	$126.85	$126.90
7 purchase totals =	$1,109.40		$1,191.2770	$1,191.27	$1,191.20	$1,191.30