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	$137.84	8.851%	$150.0402	$150.04	$150.05	$150.00
Purchase #2	$196.56	9.786%	$215.7954	$215.80	$215.80	$215.80
Purchase #3	$157.83	6.860%	$168.6571	$168.66	$168.65	$168.70
Purchase #4	$139.57	3.314%	$144.1953	$144.20	$144.20	$144.20
Purchase #5	$29.42	9.302%	$32.1566	$32.16	$32.15	$32.20
Purchase #6	$176.95	11.240%	$196.8392	$196.84	$196.85	$196.80
Purchase #7	$171.78	4.541%	$179.5805	$179.58	$179.60	$179.60
7 purchase totals =	$1,009.95		$1,087.2643	$1,087.28	$1,087.30	$1,087.30