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	$246.97	7.109%	$264.5271	$264.53	$264.55	$264.50
Purchase #2	$94.96	5.274%	$99.9682	$99.97	$99.95	$100.00
Purchase #3	$19.48	13.641%	$22.1373	$22.14	$22.15	$22.10
Purchase #4	$45.27	12.509%	$50.9328	$50.93	$50.95	$50.90
Purchase #5	$40.38	6.318%	$42.9312	$42.93	$42.95	$42.90
Purchase #6	$237.45	7.667%	$255.6553	$255.66	$255.65	$255.70
Purchase #7	$133.73	8.836%	$145.5464	$145.55	$145.55	$145.50
7 purchase totals =	$818.24		$881.6983	$881.71	$881.75	$881.60