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	$250.30	12.111%	$280.6138	$280.61	$280.60	$280.60
Purchase #2	$75.60	13.773%	$86.0124	$86.01	$86.00	$86.00
Purchase #3	$137.72	7.296%	$147.7681	$147.77	$147.75	$147.80
Purchase #4	$223.58	8.751%	$243.1455	$243.15	$243.15	$243.10
Purchase #5	$34.96	6.621%	$37.2747	$37.27	$37.25	$37.30
Purchase #6	$235.66	10.518%	$260.4467	$260.45	$260.45	$260.40
Purchase #7	$220.95	11.402%	$246.1427	$246.14	$246.15	$246.10
7 purchase totals =	$1,178.77		$1,301.4039	$1,301.40	$1,301.35	$1,301.30