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	$40.55	5.111%	$42.6225	$42.62	$42.60	$42.60
Purchase #2	$78.52	6.687%	$83.7706	$83.77	$83.75	$83.80
Purchase #3	$144.88	13.764%	$164.8213	$164.82	$164.80	$164.80
Purchase #4	$241.48	7.665%	$259.9894	$259.99	$260.00	$260.00
Purchase #5	$13.93	13.553%	$15.8179	$15.82	$15.80	$15.80
Purchase #6	$138.28	3.760%	$143.4793	$143.48	$143.50	$143.50
Purchase #7	$44.35	13.334%	$50.2636	$50.26	$50.25	$50.30
7 purchase totals =	$701.99		$760.7646	$760.76	$760.70	$760.80