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	$223.87	8.723%	$243.3982	$243.40	$243.40	$243.40
Purchase #2	$132.90	3.106%	$137.0279	$137.03	$137.05	$137.00
Purchase #3	$58.28	4.524%	$60.9166	$60.92	$60.90	$60.90
Purchase #4	$179.93	11.340%	$200.3341	$200.33	$200.35	$200.30
Purchase #5	$12.40	6.852%	$13.2496	$13.25	$13.25	$13.20
Purchase #6	$81.40	10.605%	$90.0325	$90.03	$90.05	$90.00
Purchase #7	$59.88	11.735%	$66.9069	$66.91	$66.90	$66.90
7 purchase totals =	$748.66		$811.8658	$811.87	$811.90	$811.70