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	$112.52	12.425%	$126.5006	$126.50	$126.50	$126.50
Purchase #2	$74.78	13.838%	$85.1281	$85.13	$85.15	$85.10
Purchase #3	$143.76	6.588%	$153.2309	$153.23	$153.25	$153.20
Purchase #4	$108.55	9.768%	$119.1532	$119.15	$119.15	$119.20
Purchase #5	$174.93	5.686%	$184.8765	$184.88	$184.90	$184.90
Purchase #6	$108.42	3.183%	$111.871	$111.87	$111.85	$111.90
Purchase #7	$43.81	3.260%	$45.2382	$45.24	$45.25	$45.20
7 purchase totals =	$766.77		$825.9985	$826.00	$826.05	$826.00