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	$165.99	6.864%	$177.3836	$177.38	$177.40	$177.40
Purchase #2	$131.37	4.750%	$137.6101	$137.61	$137.60	$137.60
Purchase #3	$187.82	10.527%	$207.5918	$207.59	$207.60	$207.60
Purchase #4	$76.90	10.556%	$85.0176	$85.02	$85.00	$85.00
Purchase #5	$123.93	6.585%	$132.0908	$132.09	$132.10	$132.10
Purchase #6	$82.42	9.772%	$90.4741	$90.47	$90.45	$90.50
Purchase #7	$217.37	3.208%	$224.3432	$224.34	$224.35	$224.30
7 purchase totals =	$985.80		$1,054.5112	$1,054.50	$1,054.50	$1,054.50