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	$81.78	9.521%	$89.5663	$89.57	$89.55	$89.60
Purchase #2	$146.50	6.402%	$155.8789	$155.88	$155.90	$155.90
Purchase #3	$71.63	8.280%	$77.561	$77.56	$77.55	$77.60
Purchase #4	$210.28	4.409%	$219.5512	$219.55	$219.55	$219.60
Purchase #5	$27.32	8.741%	$29.708	$29.71	$29.70	$29.70
Purchase #6	$185.90	5.798%	$196.6785	$196.68	$196.70	$196.70
Purchase #7	$104.95	8.509%	$113.8802	$113.88	$113.90	$113.90
7 purchase totals =	$828.36		$882.8241	$882.83	$882.85	$883.00