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	$118.51	10.791%	$131.2984	$131.30	$131.30	$131.30
Purchase #2	$121.62	13.173%	$137.641	$137.64	$137.65	$137.60
Purchase #3	$82.56	9.684%	$90.5551	$90.56	$90.55	$90.60
Purchase #4	$81.92	4.806%	$85.8571	$85.86	$85.85	$85.90
Purchase #5	$79.61	13.699%	$90.5158	$90.52	$90.50	$90.50
Purchase #6	$148.83	4.117%	$154.9573	$154.96	$154.95	$155.00
Purchase #7	$70.83	13.224%	$80.1966	$80.20	$80.20	$80.20
7 purchase totals =	$703.88		$771.0213	$771.04	$771.00	$771.10