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	$17.65	13.870%	$20.0981	$20.10	$20.10	$20.10
Purchase #2	$73.63	12.730%	$83.0031	$83.00	$83.00	$83.00
Purchase #3	$18.32	13.493%	$20.7919	$20.79	$20.80	$20.80
Purchase #4	$63.52	13.816%	$72.2959	$72.30	$72.30	$72.30
Purchase #5	$37.51	6.662%	$40.0089	$40.01	$40.00	$40.00
Purchase #6	$64.60	13.867%	$73.5581	$73.56	$73.55	$73.60
Purchase #7	$75.36	10.247%	$83.0821	$83.08	$83.10	$83.10
7 purchase totals =	$350.59		$392.8381	$392.84	$392.85	$392.90