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	$75.46	10.463%	$83.3554	$83.36	$83.35	$83.40
Purchase #2	$89.54	11.688%	$100.0054	$100.01	$100.00	$100.00
Purchase #3	$121.71	8.716%	$132.3182	$132.32	$132.30	$132.30
Purchase #4	$77.74	5.874%	$82.3064	$82.31	$82.30	$82.30
Purchase #5	$217.68	9.583%	$238.5403	$238.54	$238.55	$238.50
Purchase #6	$119.57	10.575%	$132.2145	$132.21	$132.20	$132.20
Purchase #7	$185.57	8.412%	$201.1801	$201.18	$201.20	$201.20
7 purchase totals =	$887.27		$969.9203	$969.93	$969.90	$969.90