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	$28.26	10.752%	$31.2985	$31.30	$31.30	$31.30
Purchase #2	$38.31	13.373%	$43.4332	$43.43	$43.45	$43.40
Purchase #3	$177.77	3.402%	$183.8177	$183.82	$183.80	$183.80
Purchase #4	$226.89	13.615%	$257.7811	$257.78	$257.80	$257.80
Purchase #5	$42.51	10.628%	$47.028	$47.03	$47.05	$47.00
Purchase #6	$37.40	10.379%	$41.2817	$41.28	$41.30	$41.30
Purchase #7	$133.37	8.619%	$144.8652	$144.87	$144.85	$144.90
7 purchase totals =	$684.51		$749.5054	$749.51	$749.55	$749.50