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	$231.44	8.660%	$251.4827	$251.48	$251.50	$251.50
Purchase #2	$239.72	6.780%	$255.973	$255.97	$255.95	$256.00
Purchase #3	$150.50	5.367%	$158.5773	$158.58	$158.60	$158.60
Purchase #4	$156.27	6.139%	$165.8634	$165.86	$165.85	$165.90
Purchase #5	$56.90	11.202%	$63.2739	$63.27	$63.25	$63.30
Purchase #6	$110.75	11.623%	$123.6225	$123.62	$123.60	$123.60
Purchase #7	$52.90	12.166%	$59.3358	$59.34	$59.35	$59.30
7 purchase totals =	$998.48		$1,078.1286	$1,078.12	$1,078.10	$1,078.20