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	$83.35	6.811%	$89.027	$89.03	$89.05	$89.00
Purchase #2	$61.83	9.208%	$67.5233	$67.52	$67.50	$67.50
Purchase #3	$81.62	13.240%	$92.4265	$92.43	$92.45	$92.40
Purchase #4	$219.31	10.227%	$241.7388	$241.74	$241.75	$241.70
Purchase #5	$6.53	3.765%	$6.7759	$6.78	$6.80	$6.80
Purchase #6	$67.29	7.870%	$72.5857	$72.59	$72.60	$72.60
Purchase #7	$160.94	6.376%	$171.2015	$171.20	$171.20	$171.20
7 purchase totals =	$680.87		$741.2787	$741.29	$741.35	$741.20