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	$36.78	12.305%	$41.3058	$41.31	$41.30	$41.30
Purchase #2	$196.81	10.383%	$217.2448	$217.24	$217.25	$217.20
Purchase #3	$68.66	13.440%	$77.8879	$77.89	$77.90	$77.90
Purchase #4	$201.96	3.442%	$208.9115	$208.91	$208.90	$208.90
Purchase #5	$100.83	3.695%	$104.5557	$104.56	$104.55	$104.60
Purchase #6	$167.35	13.467%	$189.887	$189.89	$189.90	$189.90
Purchase #7	$228.57	13.785%	$260.0784	$260.08	$260.10	$260.10
7 purchase totals =	$1,000.96		$1,099.8711	$1,099.88	$1,099.90	$1,099.90