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	$83.70	8.560%	$90.8647	$90.86	$90.85	$90.90
Purchase #2	$144.46	11.206%	$160.6482	$160.65	$160.65	$160.60
Purchase #3	$111.78	5.366%	$117.7781	$117.78	$117.80	$117.80
Purchase #4	$49.50	4.290%	$51.6236	$51.62	$51.60	$51.60
Purchase #5	$142.58	3.403%	$147.432	$147.43	$147.45	$147.40
Purchase #6	$146.47	9.653%	$160.6087	$160.61	$160.60	$160.60
Purchase #7	$39.76	4.667%	$41.6156	$41.62	$41.60	$41.60
7 purchase totals =	$718.25		$770.5709	$770.57	$770.55	$770.50