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	$158.48	13.474%	$179.8336	$179.83	$179.85	$179.80
Purchase #2	$212.87	11.147%	$236.5986	$236.60	$236.60	$236.60
Purchase #3	$85.59	3.632%	$88.6986	$88.70	$88.70	$88.70
Purchase #4	$115.86	9.524%	$126.8945	$126.89	$126.90	$126.90
Purchase #5	$233.82	3.158%	$241.204	$241.20	$241.20	$241.20
Purchase #6	$62.54	13.331%	$70.8772	$70.88	$70.90	$70.90
Purchase #7	$51.38	4.260%	$53.5688	$53.57	$53.55	$53.60
7 purchase totals =	$920.54		$997.6753	$997.67	$997.70	$997.70