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	$59.58	8.499%	$64.6437	$64.64	$64.65	$64.60
Purchase #2	$80.89	10.171%	$89.1173	$89.12	$89.10	$89.10
Purchase #3	$241.77	3.125%	$249.3253	$249.33	$249.35	$249.30
Purchase #4	$224.93	13.818%	$256.0108	$256.01	$256.00	$256.00
Purchase #5	$167.77	8.587%	$182.1764	$182.18	$182.20	$182.20
Purchase #6	$89.43	11.828%	$100.0078	$100.01	$100.00	$100.00
Purchase #7	$17.57	3.180%	$18.1287	$18.13	$18.15	$18.10
7 purchase totals =	$881.94		$959.4100	$959.42	$959.45	$959.30