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	$57.32	12.308%	$64.3749	$64.37	$64.35	$64.40
Purchase #2	$103.48	4.345%	$107.9762	$107.98	$108.00	$108.00
Purchase #3	$153.59	9.309%	$167.8877	$167.89	$167.90	$167.90
Purchase #4	$198.64	10.672%	$219.8389	$219.84	$219.85	$219.80
Purchase #5	$176.42	9.299%	$192.8253	$192.83	$192.85	$192.80
Purchase #6	$69.45	4.346%	$72.4683	$72.47	$72.45	$72.50
Purchase #7	$61.64	3.440%	$63.7604	$63.76	$63.75	$63.80
7 purchase totals =	$820.54		$889.1317	$889.14	$889.15	$889.20