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	$96.31	3.822%	$99.991	$99.99	$100.00	$100.00
Purchase #2	$196.64	9.520%	$215.3601	$215.36	$215.35	$215.40
Purchase #3	$80.48	11.265%	$89.5461	$89.55	$89.55	$89.50
Purchase #4	$224.44	12.104%	$251.6062	$251.61	$251.60	$251.60
Purchase #5	$141.51	11.789%	$158.1926	$158.19	$158.20	$158.20
Purchase #6	$60.87	5.477%	$64.2038	$64.20	$64.20	$64.20
Purchase #7	$233.27	11.638%	$260.418	$260.42	$260.40	$260.40
7 purchase totals =	$1,033.52		$1,139.3178	$1,139.32	$1,139.30	$1,139.30