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	$239.51	3.674%	$248.3096	$248.31	$248.30	$248.30
Purchase #2	$197.86	10.709%	$219.0488	$219.05	$219.05	$219.00
Purchase #3	$123.89	13.368%	$140.4516	$140.45	$140.45	$140.50
Purchase #4	$38.40	9.247%	$41.9508	$41.95	$41.95	$42.00
Purchase #5	$86.63	3.228%	$89.4264	$89.43	$89.45	$89.40
Purchase #6	$62.50	13.735%	$71.0844	$71.08	$71.10	$71.10
Purchase #7	$181.85	8.233%	$196.8217	$196.82	$196.80	$196.80
7 purchase totals =	$930.64		$1,007.0933	$1,007.09	$1,007.10	$1,007.10