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	$53.49	5.324%	$56.3378	$56.34	$56.35	$56.30
Purchase #2	$46.94	13.610%	$53.3285	$53.33	$53.35	$53.30
Purchase #3	$178.60	5.698%	$188.7766	$188.78	$188.80	$188.80
Purchase #4	$71.61	12.200%	$80.3464	$80.35	$80.35	$80.30
Purchase #5	$40.59	6.243%	$43.124	$43.12	$43.10	$43.10
Purchase #6	$150.76	6.127%	$159.9971	$160.00	$160.00	$160.00
Purchase #7	$41.32	6.393%	$43.9616	$43.96	$43.95	$44.00
7 purchase totals =	$583.31		$625.8720	$625.88	$625.90	$625.80