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	$250.95	11.796%	$280.5521	$280.55	$280.55	$280.60
Purchase #2	$231.40	4.533%	$241.8894	$241.89	$241.90	$241.90
Purchase #3	$129.39	3.667%	$134.1347	$134.13	$134.15	$134.10
Purchase #4	$124.91	7.681%	$134.5043	$134.50	$134.50	$134.50
Purchase #5	$80.83	9.595%	$88.5856	$88.59	$88.60	$88.60
Purchase #6	$75.89	12.132%	$85.097	$85.10	$85.10	$85.10
Purchase #7	$233.96	3.230%	$241.5169	$241.52	$241.50	$241.50
7 purchase totals =	$1,127.33		$1,206.2800	$1,206.28	$1,206.30	$1,206.30