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	$36.79	6.368%	$39.1328	$39.13	$39.15	$39.10
Purchase #2	$106.46	4.340%	$111.0804	$111.08	$111.10	$111.10
Purchase #3	$100.79	11.462%	$112.3425	$112.34	$112.35	$112.30
Purchase #4	$215.97	12.202%	$242.3227	$242.32	$242.30	$242.30
Purchase #5	$98.99	12.732%	$111.5934	$111.59	$111.60	$111.60
Purchase #6	$214.26	10.376%	$236.4916	$236.49	$236.50	$236.50
Purchase #7	$135.65	7.830%	$146.2714	$146.27	$146.25	$146.30
7 purchase totals =	$908.91		$999.2348	$999.22	$999.25	$999.20