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	$172.28	5.377%	$181.5435	$181.54	$181.55	$181.50
Purchase #2	$164.44	11.227%	$182.9017	$182.90	$182.90	$182.90
Purchase #3	$124.46	10.782%	$137.8793	$137.88	$137.90	$137.90
Purchase #4	$83.77	3.177%	$86.4314	$86.43	$86.45	$86.40
Purchase #5	$167.91	8.105%	$181.5191	$181.52	$181.50	$181.50
Purchase #6	$175.70	8.521%	$190.6714	$190.67	$190.65	$190.70
Purchase #7	$117.72	11.248%	$130.9611	$130.96	$130.95	$131.00
7 purchase totals =	$1,006.28		$1,091.9075	$1,091.90	$1,091.90	$1,091.90