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	$115.85	6.610%	$123.5077	$123.51	$123.50	$123.50
Purchase #2	$161.96	13.707%	$184.1599	$184.16	$184.15	$184.20
Purchase #3	$132.71	11.869%	$148.4613	$148.46	$148.45	$148.50
Purchase #4	$132.69	5.557%	$140.0636	$140.06	$140.05	$140.10
Purchase #5	$192.46	8.235%	$208.3091	$208.31	$208.30	$208.30
Purchase #6	$142.85	4.609%	$149.434	$149.43	$149.45	$149.40
Purchase #7	$226.79	12.868%	$255.9733	$255.97	$255.95	$256.00
7 purchase totals =	$1,105.31		$1,209.9089	$1,209.90	$1,209.85	$1,210.00