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	$137.69	4.739%	$144.2151	$144.22	$144.20	$144.20
Purchase #2	$54.82	8.602%	$59.5356	$59.54	$59.55	$59.50
Purchase #3	$195.32	5.632%	$206.3204	$206.32	$206.30	$206.30
Purchase #4	$140.53	3.536%	$145.4991	$145.50	$145.50	$145.50
Purchase #5	$194.70	10.480%	$215.1046	$215.10	$215.10	$215.10
Purchase #6	$89.91	8.403%	$97.4651	$97.47	$97.45	$97.50
Purchase #7	$56.84	10.724%	$62.9355	$62.94	$62.95	$62.90
7 purchase totals =	$869.81		$931.0754	$931.09	$931.05	$931.00