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	$66.33	10.256%	$73.1328	$73.13	$73.15	$73.10
Purchase #2	$44.26	13.796%	$50.3661	$50.37	$50.35	$50.40
Purchase #3	$124.59	11.241%	$138.5952	$138.60	$138.60	$138.60
Purchase #4	$213.58	5.789%	$225.9441	$225.94	$225.95	$225.90
Purchase #5	$146.93	3.792%	$152.5016	$152.50	$152.50	$152.50
Purchase #6	$77.88	6.759%	$83.1439	$83.14	$83.15	$83.10
Purchase #7	$106.43	6.725%	$113.5874	$113.59	$113.60	$113.60
7 purchase totals =	$780.00		$837.2711	$837.27	$837.30	$837.20