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	$127.45	9.548%	$139.6189	$139.62	$139.60	$139.60
Purchase #2	$176.33	7.794%	$190.0732	$190.07	$190.05	$190.10
Purchase #3	$132.69	3.433%	$137.2452	$137.25	$137.25	$137.20
Purchase #4	$213.88	4.706%	$223.9452	$223.95	$223.95	$223.90
Purchase #5	$126.68	12.673%	$142.7342	$142.73	$142.75	$142.70
Purchase #6	$122.80	6.732%	$131.0669	$131.07	$131.05	$131.10
Purchase #7	$115.78	10.429%	$127.8547	$127.85	$127.85	$127.90
7 purchase totals =	$1,015.61		$1,092.5383	$1,092.54	$1,092.50	$1,092.50