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	$241.79	12.254%	$271.4189	$271.42	$271.40	$271.40
Purchase #2	$225.44	3.382%	$233.0644	$233.06	$233.05	$233.10
Purchase #3	$51.90	6.458%	$55.2517	$55.25	$55.25	$55.30
Purchase #4	$189.62	3.551%	$196.3534	$196.35	$196.35	$196.40
Purchase #5	$81.77	8.388%	$88.6289	$88.63	$88.65	$88.60
Purchase #6	$123.78	11.614%	$138.1558	$138.16	$138.15	$138.20
Purchase #7	$174.72	3.823%	$181.3995	$181.40	$181.40	$181.40
7 purchase totals =	$1,089.02		$1,164.2726	$1,164.27	$1,164.25	$1,164.40