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	$203.77	13.632%	$231.5479	$231.55	$231.55	$231.50
Purchase #2	$30.45	12.465%	$34.2456	$34.25	$34.25	$34.20
Purchase #3	$167.78	11.411%	$186.9254	$186.93	$186.95	$186.90
Purchase #4	$104.42	6.357%	$111.058	$111.06	$111.05	$111.10
Purchase #5	$147.30	8.171%	$159.3359	$159.34	$159.35	$159.30
Purchase #6	$66.93	7.420%	$71.8962	$71.90	$71.90	$71.90
Purchase #7	$192.85	6.758%	$205.8828	$205.88	$205.90	$205.90
7 purchase totals =	$913.50		$1,000.8918	$1,000.91	$1,000.95	$1,000.80