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	$80.42	11.358%	$89.5541	$89.55	$89.55	$89.60
Purchase #2	$162.47	7.653%	$174.9038	$174.90	$174.90	$174.90
Purchase #3	$47.67	7.152%	$51.0794	$51.08	$51.10	$51.10
Purchase #4	$183.94	11.652%	$205.3727	$205.37	$205.35	$205.40
Purchase #5	$180.50	8.596%	$196.0158	$196.02	$196.00	$196.00
Purchase #6	$176.87	3.703%	$183.4195	$183.42	$183.40	$183.40
Purchase #7	$81.51	6.779%	$87.0356	$87.04	$87.05	$87.00
7 purchase totals =	$913.38		$987.3809	$987.38	$987.35	$987.40