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	$135.81	4.762%	$142.2773	$142.28	$142.30	$142.30
Purchase #2	$146.42	6.352%	$155.7206	$155.72	$155.70	$155.70
Purchase #3	$155.56	12.308%	$174.7063	$174.71	$174.70	$174.70
Purchase #4	$126.74	4.313%	$132.2063	$132.21	$132.20	$132.20
Purchase #5	$50.60	9.410%	$55.3615	$55.36	$55.35	$55.40
Purchase #6	$66.96	7.206%	$71.7851	$71.79	$71.80	$71.80
Purchase #7	$38.25	10.801%	$42.3814	$42.38	$42.40	$42.40
7 purchase totals =	$720.34		$774.4385	$774.45	$774.45	$774.50