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	$50.36	7.863%	$54.3198	$54.32	$54.30	$54.30
Purchase #2	$198.56	5.316%	$209.1154	$209.12	$209.10	$209.10
Purchase #3	$18.78	12.564%	$21.1395	$21.14	$21.15	$21.10
Purchase #4	$42.86	12.166%	$48.0743	$48.07	$48.05	$48.10
Purchase #5	$48.95	4.205%	$51.0083	$51.01	$51.00	$51.00
Purchase #6	$175.86	3.751%	$182.4565	$182.46	$182.45	$182.50
Purchase #7	$42.68	8.382%	$46.2574	$46.26	$46.25	$46.30
7 purchase totals =	$578.05		$612.3712	$612.38	$612.30	$612.40