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	$242.93	7.314%	$260.6979	$260.70	$260.70	$260.70
Purchase #2	$224.92	11.365%	$250.4822	$250.48	$250.50	$250.50
Purchase #3	$179.30	6.181%	$190.3825	$190.38	$190.40	$190.40
Purchase #4	$176.53	4.726%	$184.8728	$184.87	$184.85	$184.90
Purchase #5	$72.86	7.860%	$78.5868	$78.59	$78.60	$78.60
Purchase #6	$199.36	13.517%	$226.3075	$226.31	$226.30	$226.30
Purchase #7	$154.32	6.804%	$164.8199	$164.82	$164.80	$164.80
7 purchase totals =	$1,250.22		$1,356.1496	$1,356.15	$1,356.15	$1,356.20