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	$40.87	9.619%	$44.8013	$44.80	$44.80	$44.80
Purchase #2	$50.52	4.297%	$52.6908	$52.69	$52.70	$52.70
Purchase #3	$168.83	3.555%	$174.8319	$174.83	$174.85	$174.80
Purchase #4	$89.67	8.409%	$97.2104	$97.21	$97.20	$97.20
Purchase #5	$122.74	13.652%	$139.4965	$139.50	$139.50	$139.50
Purchase #6	$90.87	13.697%	$103.3165	$103.32	$103.30	$103.30
Purchase #7	$28.91	10.411%	$31.9198	$31.92	$31.90	$31.90
7 purchase totals =	$592.41		$644.2672	$644.27	$644.25	$644.20