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	$37.97	7.660%	$40.8785	$40.88	$40.90	$40.90
Purchase #2	$177.86	8.463%	$192.9123	$192.91	$192.90	$192.90
Purchase #3	$18.77	10.590%	$20.7577	$20.76	$20.75	$20.80
Purchase #4	$55.78	6.768%	$59.5552	$59.56	$59.55	$59.60
Purchase #5	$92.80	12.547%	$104.4436	$104.44	$104.45	$104.40
Purchase #6	$98.93	4.191%	$103.0762	$103.08	$103.10	$103.10
Purchase #7	$176.42	3.353%	$182.3354	$182.34	$182.35	$182.30
7 purchase totals =	$658.53		$703.9589	$703.97	$704.00	$704.00