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	$136.26	13.464%	$154.606	$154.61	$154.60	$154.60
Purchase #2	$114.83	4.510%	$120.0088	$120.01	$120.00	$120.00
Purchase #3	$175.90	4.249%	$183.374	$183.37	$183.35	$183.40
Purchase #4	$94.42	13.829%	$107.4773	$107.48	$107.50	$107.50
Purchase #5	$183.74	3.410%	$190.0055	$190.01	$190.00	$190.00
Purchase #6	$76.71	7.661%	$82.5868	$82.59	$82.60	$82.60
Purchase #7	$247.35	7.290%	$265.3818	$265.38	$265.40	$265.40
7 purchase totals =	$1,029.21		$1,103.4402	$1,103.45	$1,103.45	$1,103.50