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	$38.80	11.262%	$43.1697	$43.17	$43.15	$43.20
Purchase #2	$130.51	6.737%	$139.3025	$139.30	$139.30	$139.30
Purchase #3	$104.65	6.606%	$111.5632	$111.56	$111.55	$111.60
Purchase #4	$27.90	4.382%	$29.1226	$29.12	$29.10	$29.10
Purchase #5	$119.76	8.562%	$130.0139	$130.01	$130.00	$130.00
Purchase #6	$148.36	10.768%	$164.3354	$164.34	$164.35	$164.30
Purchase #7	$219.92	13.255%	$249.0704	$249.07	$249.05	$249.10
7 purchase totals =	$789.90		$866.5777	$866.57	$866.50	$866.60