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	$36.38	3.296%	$37.5791	$37.58	$37.60	$37.60
Purchase #2	$16.99	9.260%	$18.5633	$18.56	$18.55	$18.60
Purchase #3	$39.72	8.395%	$43.0545	$43.05	$43.05	$43.10
Purchase #4	$118.45	4.584%	$123.8797	$123.88	$123.90	$123.90
Purchase #5	$98.35	3.796%	$102.0834	$102.08	$102.10	$102.10
Purchase #6	$12.32	10.828%	$13.654	$13.65	$13.65	$13.70
Purchase #7	$208.74	4.859%	$218.8827	$218.88	$218.90	$218.90
7 purchase totals =	$530.95		$557.6967	$557.68	$557.75	$557.90