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	$194.49	10.782%	$215.4599	$215.46	$215.45	$215.50
Purchase #2	$21.80	8.227%	$23.5935	$23.59	$23.60	$23.60
Purchase #3	$136.56	10.183%	$150.4659	$150.47	$150.45	$150.50
Purchase #4	$216.98	3.642%	$224.8824	$224.88	$224.90	$224.90
Purchase #5	$9.81	13.176%	$11.1026	$11.10	$11.10	$11.10
Purchase #6	$123.45	3.554%	$127.8374	$127.84	$127.85	$127.80
Purchase #7	$88.86	10.537%	$98.2232	$98.22	$98.20	$98.20
7 purchase totals =	$791.95		$851.5649	$851.56	$851.55	$851.60