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	$81.96	9.336%	$89.6118	$89.61	$89.60	$89.60
Purchase #2	$81.59	5.629%	$86.1827	$86.18	$86.20	$86.20
Purchase #3	$190.94	10.662%	$211.298	$211.30	$211.30	$211.30
Purchase #4	$181.39	13.486%	$205.8523	$205.85	$205.85	$205.90
Purchase #5	$41.30	4.192%	$43.0313	$43.03	$43.05	$43.00
Purchase #6	$152.63	6.458%	$162.4868	$162.49	$162.50	$162.50
Purchase #7	$130.42	5.150%	$137.1366	$137.14	$137.15	$137.10
7 purchase totals =	$860.23		$935.5995	$935.60	$935.65	$935.60