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	$164.37	7.690%	$177.0101	$177.01	$177.00	$177.00
Purchase #2	$179.82	10.365%	$198.4583	$198.46	$198.45	$198.50
Purchase #3	$162.53	10.677%	$179.8833	$179.88	$179.90	$179.90
Purchase #4	$94.71	8.155%	$102.4336	$102.43	$102.45	$102.40
Purchase #5	$168.67	11.212%	$187.5813	$187.58	$187.60	$187.60
Purchase #6	$225.60	13.166%	$255.3025	$255.30	$255.30	$255.30
Purchase #7	$175.82	7.654%	$189.2773	$189.28	$189.30	$189.30
7 purchase totals =	$1,171.52		$1,289.9464	$1,289.94	$1,290.00	$1,290.00