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	$248.54	11.257%	$276.5181	$276.52	$276.50	$276.50
Purchase #2	$209.62	11.533%	$233.7955	$233.80	$233.80	$233.80
Purchase #3	$108.38	8.560%	$117.6573	$117.66	$117.65	$117.70
Purchase #4	$109.83	8.654%	$119.3347	$119.33	$119.35	$119.30
Purchase #5	$208.78	6.664%	$222.6931	$222.69	$222.70	$222.70
Purchase #6	$19.50	4.773%	$20.4307	$20.43	$20.45	$20.40
Purchase #7	$59.78	12.139%	$67.0367	$67.04	$67.05	$67.00
7 purchase totals =	$964.43		$1,057.4661	$1,057.47	$1,057.50	$1,057.40