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	$235.43	13.369%	$266.9046	$266.90	$266.90	$266.90
Purchase #2	$38.76	4.574%	$40.5329	$40.53	$40.55	$40.50
Purchase #3	$89.31	11.428%	$99.5163	$99.52	$99.50	$99.50
Purchase #4	$108.82	3.613%	$112.7517	$112.75	$112.75	$112.80
Purchase #5	$92.26	5.349%	$97.195	$97.20	$97.20	$97.20
Purchase #6	$173.79	5.794%	$183.8594	$183.86	$183.85	$183.90
Purchase #7	$98.51	6.450%	$104.8639	$104.86	$104.85	$104.90
7 purchase totals =	$836.88		$905.6238	$905.62	$905.60	$905.70