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	$34.29	10.168%	$37.7766	$37.78	$37.80	$37.80
Purchase #2	$13.27	3.569%	$13.7436	$13.74	$13.75	$13.70
Purchase #3	$98.41	12.376%	$110.5892	$110.59	$110.60	$110.60
Purchase #4	$119.56	10.866%	$132.5514	$132.55	$132.55	$132.60
Purchase #5	$116.91	12.840%	$131.9212	$131.92	$131.90	$131.90
Purchase #6	$155.66	13.169%	$176.1589	$176.16	$176.15	$176.20
Purchase #7	$58.71	3.430%	$60.7238	$60.72	$60.70	$60.70
7 purchase totals =	$596.81		$663.4647	$663.46	$663.45	$663.50