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	$29.32	10.708%	$32.4596	$32.46	$32.45	$32.50
Purchase #2	$51.63	8.640%	$56.0908	$56.09	$56.10	$56.10
Purchase #3	$81.27	6.464%	$86.5233	$86.52	$86.50	$86.50
Purchase #4	$52.43	7.387%	$56.303	$56.30	$56.30	$56.30
Purchase #5	$161.94	10.106%	$178.3057	$178.31	$178.30	$178.30
Purchase #6	$145.92	11.169%	$162.2178	$162.22	$162.20	$162.20
Purchase #7	$216.79	3.548%	$224.4817	$224.48	$224.50	$224.50
7 purchase totals =	$739.30		$796.3819	$796.38	$796.35	$796.40