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	$15.54	13.296%	$17.6062	$17.61	$17.60	$17.60
Purchase #2	$204.63	5.469%	$215.8212	$215.82	$215.80	$215.80
Purchase #3	$204.90	10.161%	$225.7199	$225.72	$225.70	$225.70
Purchase #4	$13.36	7.280%	$14.3326	$14.33	$14.35	$14.30
Purchase #5	$100.38	9.223%	$109.638	$109.64	$109.65	$109.60
Purchase #6	$127.93	11.257%	$142.3311	$142.33	$142.35	$142.30
Purchase #7	$115.97	4.183%	$120.821	$120.82	$120.80	$120.80
7 purchase totals =	$782.71		$846.2700	$846.27	$846.25	$846.10