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	$132.50	3.734%	$137.4476	$137.45	$137.45	$137.40
Purchase #2	$180.70	8.536%	$196.1246	$196.12	$196.10	$196.10
Purchase #3	$66.58	9.780%	$73.0915	$73.09	$73.10	$73.10
Purchase #4	$210.35	13.189%	$238.0931	$238.09	$238.10	$238.10
Purchase #5	$78.90	12.411%	$88.6923	$88.69	$88.70	$88.70
Purchase #6	$241.59	11.645%	$269.7232	$269.72	$269.70	$269.70
Purchase #7	$91.83	5.425%	$96.8118	$96.81	$96.80	$96.80
7 purchase totals =	$1,002.45		$1,099.9841	$1,099.97	$1,099.95	$1,099.90