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	$64.56	11.810%	$72.1845	$72.18	$72.20	$72.20
Purchase #2	$148.90	10.711%	$164.8487	$164.85	$164.85	$164.80
Purchase #3	$197.28	13.783%	$224.4711	$224.47	$224.45	$224.50
Purchase #4	$81.80	8.631%	$88.8602	$88.86	$88.85	$88.90
Purchase #5	$42.34	6.813%	$45.2246	$45.22	$45.20	$45.20
Purchase #6	$39.55	4.346%	$41.2688	$41.27	$41.25	$41.30
Purchase #7	$222.35	3.857%	$230.926	$230.93	$230.95	$230.90
7 purchase totals =	$796.78		$867.7839	$867.78	$867.75	$867.80