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	$46.41	11.626%	$51.8056	$51.81	$51.80	$51.80
Purchase #2	$130.70	9.636%	$143.2943	$143.29	$143.30	$143.30
Purchase #3	$247.84	12.295%	$278.3119	$278.31	$278.30	$278.30
Purchase #4	$203.42	3.418%	$210.3729	$210.37	$210.35	$210.40
Purchase #5	$70.33	11.681%	$78.5452	$78.55	$78.55	$78.50
Purchase #6	$90.31	6.335%	$96.0311	$96.03	$96.05	$96.00
Purchase #7	$206.47	10.545%	$228.2423	$228.24	$228.25	$228.20
7 purchase totals =	$995.48		$1,086.6033	$1,086.60	$1,086.60	$1,086.50