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	$239.90	6.378%	$255.2008	$255.20	$255.20	$255.20
Purchase #2	$136.56	13.579%	$155.1035	$155.10	$155.10	$155.10
Purchase #3	$249.42	9.190%	$272.3417	$272.34	$272.35	$272.30
Purchase #4	$38.50	7.210%	$41.2759	$41.28	$41.30	$41.30
Purchase #5	$157.39	6.246%	$167.2206	$167.22	$167.20	$167.20
Purchase #6	$96.45	6.306%	$102.5321	$102.53	$102.55	$102.50
Purchase #7	$37.94	12.804%	$42.7978	$42.80	$42.80	$42.80
7 purchase totals =	$956.16		$1,036.4724	$1,036.47	$1,036.50	$1,036.40