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	$164.79	12.762%	$185.8205	$185.82	$185.80	$185.80
Purchase #2	$139.45	5.373%	$146.9426	$146.94	$146.95	$146.90
Purchase #3	$159.83	11.138%	$177.6319	$177.63	$177.65	$177.60
Purchase #4	$38.72	4.710%	$40.5437	$40.54	$40.55	$40.50
Purchase #5	$240.77	5.852%	$254.8599	$254.86	$254.85	$254.90
Purchase #6	$145.41	3.171%	$150.021	$150.02	$150.00	$150.00
Purchase #7	$169.74	4.130%	$176.7503	$176.75	$176.75	$176.80
7 purchase totals =	$1,058.71		$1,132.5699	$1,132.56	$1,132.55	$1,132.50