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	$111.70	8.852%	$121.5877	$121.59	$121.60	$121.60
Purchase #2	$73.81	5.706%	$78.0216	$78.02	$78.00	$78.00
Purchase #3	$109.84	12.185%	$123.224	$123.22	$123.20	$123.20
Purchase #4	$217.42	4.271%	$226.706	$226.71	$226.70	$226.70
Purchase #5	$124.34	12.377%	$139.7296	$139.73	$139.75	$139.70
Purchase #6	$234.71	10.610%	$259.6127	$259.61	$259.60	$259.60
Purchase #7	$228.67	11.534%	$255.0448	$255.04	$255.05	$255.00
7 purchase totals =	$1,100.49		$1,203.9264	$1,203.92	$1,203.90	$1,203.80