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	$151.53	9.804%	$166.386	$166.39	$166.40	$166.40
Purchase #2	$80.72	9.519%	$88.4037	$88.40	$88.40	$88.40
Purchase #3	$104.58	6.867%	$111.7615	$111.76	$111.75	$111.80
Purchase #4	$155.45	4.469%	$162.3971	$162.40	$162.40	$162.40
Purchase #5	$94.60	5.508%	$99.8106	$99.81	$99.80	$99.80
Purchase #6	$146.58	4.756%	$153.5513	$153.55	$153.55	$153.60
Purchase #7	$15.75	5.214%	$16.5712	$16.57	$16.55	$16.60
7 purchase totals =	$749.21		$798.8814	$798.88	$798.85	$799.00