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	$151.35	9.564%	$165.8251	$165.83	$165.85	$165.80
Purchase #2	$99.45	3.477%	$102.9079	$102.91	$102.90	$102.90
Purchase #3	$30.31	3.106%	$31.2514	$31.25	$31.25	$31.30
Purchase #4	$114.40	11.476%	$127.5285	$127.53	$127.55	$127.50
Purchase #5	$186.25	6.418%	$198.2035	$198.20	$198.20	$198.20
Purchase #6	$175.64	13.765%	$199.8168	$199.82	$199.80	$199.80
Purchase #7	$148.84	10.853%	$164.9936	$164.99	$165.00	$165.00
7 purchase totals =	$906.24		$990.5268	$990.53	$990.55	$990.50