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	$127.58	3.540%	$132.0963	$132.10	$132.10	$132.10
Purchase #2	$116.77	8.498%	$126.6931	$126.69	$126.70	$126.70
Purchase #3	$192.90	7.790%	$207.9269	$207.93	$207.95	$207.90
Purchase #4	$82.68	8.158%	$89.425	$89.43	$89.45	$89.40
Purchase #5	$188.59	10.429%	$208.2581	$208.26	$208.25	$208.30
Purchase #6	$35.83	12.573%	$40.3349	$40.33	$40.35	$40.30
Purchase #7	$145.94	4.705%	$152.8065	$152.81	$152.80	$152.80
7 purchase totals =	$890.29		$957.5408	$957.55	$957.60	$957.50