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	$19.44	3.231%	$20.0681	$20.07	$20.05	$20.10
Purchase #2	$155.94	11.114%	$173.2712	$173.27	$173.25	$173.30
Purchase #3	$143.64	4.849%	$150.6051	$150.61	$150.60	$150.60
Purchase #4	$130.91	10.330%	$144.433	$144.43	$144.45	$144.40
Purchase #5	$117.98	10.682%	$130.5826	$130.58	$130.60	$130.60
Purchase #6	$185.81	5.693%	$196.3882	$196.39	$196.40	$196.40
Purchase #7	$73.97	9.391%	$80.9165	$80.92	$80.90	$80.90
7 purchase totals =	$827.69		$896.2647	$896.27	$896.25	$896.30