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	$34.76	9.189%	$37.9541	$37.95	$37.95	$38.00
Purchase #2	$119.80	8.731%	$130.2597	$130.26	$130.25	$130.30
Purchase #3	$190.67	8.292%	$206.4804	$206.48	$206.50	$206.50
Purchase #4	$14.52	6.268%	$15.4301	$15.43	$15.45	$15.40
Purchase #5	$53.37	11.120%	$59.3047	$59.30	$59.30	$59.30
Purchase #6	$117.64	12.645%	$132.5156	$132.52	$132.50	$132.50
Purchase #7	$143.78	8.701%	$156.2903	$156.29	$156.30	$156.30
7 purchase totals =	$674.54		$738.2349	$738.23	$738.25	$738.30