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	$127.88	13.774%	$145.4942	$145.49	$145.50	$145.50
Purchase #2	$238.85	10.210%	$263.2366	$263.24	$263.25	$263.20
Purchase #3	$28.28	11.392%	$31.5017	$31.50	$31.50	$31.50
Purchase #4	$76.47	9.624%	$83.8295	$83.83	$83.85	$83.80
Purchase #5	$169.36	12.277%	$190.1523	$190.15	$190.15	$190.20
Purchase #6	$241.73	6.102%	$256.4804	$256.48	$256.50	$256.50
Purchase #7	$132.61	12.465%	$149.1398	$149.14	$149.15	$149.10
7 purchase totals =	$1,015.18		$1,119.8345	$1,119.83	$1,119.90	$1,119.80