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	$238.86	6.866%	$255.2601	$255.26	$255.25	$255.30
Purchase #2	$79.94	10.656%	$88.4584	$88.46	$88.45	$88.50
Purchase #3	$107.89	3.196%	$111.3382	$111.34	$111.35	$111.30
Purchase #4	$129.25	6.646%	$137.84	$137.84	$137.85	$137.80
Purchase #5	$202.70	9.647%	$222.2545	$222.25	$222.25	$222.30
Purchase #6	$80.37	12.228%	$90.1976	$90.20	$90.20	$90.20
Purchase #7	$189.32	12.518%	$213.0191	$213.02	$213.00	$213.00
7 purchase totals =	$1,028.33		$1,118.3679	$1,118.37	$1,118.35	$1,118.40