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	$161.39	4.385%	$168.467	$168.47	$168.45	$168.50
Purchase #2	$95.88	5.156%	$100.8236	$100.82	$100.80	$100.80
Purchase #3	$220.49	7.621%	$237.2935	$237.29	$237.30	$237.30
Purchase #4	$196.55	13.704%	$223.4852	$223.49	$223.50	$223.50
Purchase #5	$78.36	6.177%	$83.2003	$83.20	$83.20	$83.20
Purchase #6	$138.31	3.489%	$143.1356	$143.14	$143.15	$143.10
Purchase #7	$30.70	10.316%	$33.867	$33.87	$33.85	$33.90
7 purchase totals =	$921.68		$990.2722	$990.28	$990.25	$990.30