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	$115.33	13.693%	$131.1221	$131.12	$131.10	$131.10
Purchase #2	$41.30	9.674%	$45.2954	$45.30	$45.30	$45.30
Purchase #3	$58.33	5.144%	$61.3305	$61.33	$61.35	$61.30
Purchase #4	$14.67	9.141%	$16.011	$16.01	$16.00	$16.00
Purchase #5	$63.51	4.663%	$66.4715	$66.47	$66.45	$66.50
Purchase #6	$234.83	10.210%	$258.8061	$258.81	$258.80	$258.80
Purchase #7	$94.58	9.440%	$103.5084	$103.51	$103.50	$103.50
7 purchase totals =	$622.55		$682.5450	$682.55	$682.50	$682.50