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	$37.84	7.462%	$40.6636	$40.66	$40.65	$40.70
Purchase #2	$205.67	13.645%	$233.7337	$233.73	$233.75	$233.70
Purchase #3	$144.33	4.481%	$150.7974	$150.80	$150.80	$150.80
Purchase #4	$190.69	13.224%	$215.9068	$215.91	$215.90	$215.90
Purchase #5	$126.81	3.616%	$131.3954	$131.40	$131.40	$131.40
Purchase #6	$121.81	8.570%	$132.2491	$132.25	$132.25	$132.20
Purchase #7	$15.89	4.384%	$16.5866	$16.59	$16.60	$16.60
7 purchase totals =	$843.04		$921.3326	$921.34	$921.35	$921.30