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	$162.50	11.250%	$180.7813	$180.78	$180.80	$180.80
Purchase #2	$46.37	12.339%	$52.0916	$52.09	$52.10	$52.10
Purchase #3	$36.51	8.639%	$39.6641	$39.66	$39.65	$39.70
Purchase #4	$136.50	3.293%	$140.9949	$140.99	$141.00	$141.00
Purchase #5	$196.65	6.669%	$209.7646	$209.76	$209.75	$209.80
Purchase #6	$46.70	9.223%	$51.0071	$51.01	$51.00	$51.00
Purchase #7	$80.70	10.868%	$89.4705	$89.47	$89.45	$89.50
7 purchase totals =	$705.93		$763.7741	$763.76	$763.75	$763.90