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	$23.69	8.152%	$25.6212	$25.62	$25.60	$25.60
Purchase #2	$148.33	8.122%	$160.3774	$160.38	$160.40	$160.40
Purchase #3	$230.67	4.258%	$240.4919	$240.49	$240.50	$240.50
Purchase #4	$237.73	3.541%	$246.148	$246.15	$246.15	$246.10
Purchase #5	$99.49	12.192%	$111.6198	$111.62	$111.60	$111.60
Purchase #6	$41.39	3.587%	$42.8747	$42.87	$42.85	$42.90
Purchase #7	$82.45	9.357%	$90.1648	$90.16	$90.15	$90.20
7 purchase totals =	$863.75		$917.2978	$917.29	$917.25	$917.30