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	$72.88	10.224%	$80.3313	$80.33	$80.35	$80.30
Purchase #2	$107.37	5.108%	$112.8545	$112.85	$112.85	$112.90
Purchase #3	$117.70	8.398%	$127.5844	$127.58	$127.60	$127.60
Purchase #4	$40.59	4.869%	$42.5663	$42.57	$42.55	$42.60
Purchase #5	$177.27	5.222%	$186.527	$186.53	$186.55	$186.50
Purchase #6	$180.81	10.869%	$200.4622	$200.46	$200.45	$200.50
Purchase #7	$173.52	9.502%	$190.0079	$190.01	$190.00	$190.00
7 purchase totals =	$870.14		$940.3336	$940.33	$940.35	$940.40