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	$95.88	5.566%	$101.2167	$101.22	$101.20	$101.20
Purchase #2	$121.93	5.212%	$128.285	$128.29	$128.30	$128.30
Purchase #3	$108.71	4.871%	$114.0053	$114.01	$114.00	$114.00
Purchase #4	$182.33	5.187%	$191.7875	$191.79	$191.80	$191.80
Purchase #5	$73.48	7.405%	$78.9212	$78.92	$78.90	$78.90
Purchase #6	$18.37	6.845%	$19.6274	$19.63	$19.65	$19.60
Purchase #7	$37.25	3.265%	$38.4662	$38.47	$38.45	$38.50
7 purchase totals =	$637.95		$672.3093	$672.33	$672.30	$672.30