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	$81.91	10.854%	$90.8005	$90.80	$90.80	$90.80
Purchase #2	$242.41	13.385%	$274.8566	$274.86	$274.85	$274.90
Purchase #3	$73.30	9.763%	$80.4563	$80.46	$80.45	$80.50
Purchase #4	$68.91	10.306%	$76.0119	$76.01	$76.00	$76.00
Purchase #5	$167.78	11.238%	$186.6351	$186.64	$186.65	$186.60
Purchase #6	$180.98	4.799%	$189.6652	$189.67	$189.65	$189.70
Purchase #7	$152.84	13.436%	$173.3756	$173.38	$173.40	$173.40
7 purchase totals =	$968.13		$1,071.8012	$1,071.82	$1,071.80	$1,071.90