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	$92.93	8.186%	$100.5372	$100.54	$100.55	$100.50
Purchase #2	$32.50	11.165%	$36.1286	$36.13	$36.15	$36.10
Purchase #3	$154.34	11.267%	$171.7295	$171.73	$171.75	$171.70
Purchase #4	$164.26	9.199%	$179.3703	$179.37	$179.35	$179.40
Purchase #5	$201.85	3.339%	$208.5898	$208.59	$208.60	$208.60
Purchase #6	$105.29	6.178%	$111.7948	$111.79	$111.80	$111.80
Purchase #7	$13.74	5.284%	$14.466	$14.47	$14.45	$14.50
7 purchase totals =	$764.91		$822.6162	$822.62	$822.65	$822.60