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	$133.54	6.850%	$142.6875	$142.69	$142.70	$142.70
Purchase #2	$239.30	4.302%	$249.5947	$249.59	$249.60	$249.60
Purchase #3	$128.53	6.217%	$136.5207	$136.52	$136.50	$136.50
Purchase #4	$184.45	7.291%	$197.8982	$197.90	$197.90	$197.90
Purchase #5	$231.52	4.296%	$241.4661	$241.47	$241.45	$241.50
Purchase #6	$138.31	11.720%	$154.5199	$154.52	$154.50	$154.50
Purchase #7	$52.55	9.624%	$57.6074	$57.61	$57.60	$57.60
7 purchase totals =	$1,108.20		$1,180.2945	$1,180.30	$1,180.25	$1,180.30