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	$126.35	8.259%	$136.7852	$136.79	$136.80	$136.80
Purchase #2	$89.64	10.587%	$99.1302	$99.13	$99.15	$99.10
Purchase #3	$37.51	6.788%	$40.0562	$40.06	$40.05	$40.10
Purchase #4	$187.96	6.863%	$200.8597	$200.86	$200.85	$200.90
Purchase #5	$90.98	12.588%	$102.4326	$102.43	$102.45	$102.40
Purchase #6	$235.29	11.337%	$261.9648	$261.96	$261.95	$262.00
Purchase #7	$113.95	4.648%	$119.2464	$119.25	$119.25	$119.20
7 purchase totals =	$881.68		$960.4751	$960.48	$960.50	$960.50