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	$78.28	13.483%	$88.8345	$88.83	$88.85	$88.80
Purchase #2	$201.97	10.773%	$223.7282	$223.73	$223.75	$223.70
Purchase #3	$94.33	9.615%	$103.3998	$103.40	$103.40	$103.40
Purchase #4	$247.54	7.641%	$266.4545	$266.45	$266.45	$266.50
Purchase #5	$173.38	3.839%	$180.0361	$180.04	$180.05	$180.00
Purchase #6	$105.94	4.777%	$111.0008	$111.00	$111.00	$111.00
Purchase #7	$20.67	5.340%	$21.7738	$21.77	$21.75	$21.80
7 purchase totals =	$922.11		$995.2277	$995.22	$995.25	$995.20