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	$131.53	3.758%	$136.4729	$136.47	$136.45	$136.50
Purchase #2	$145.77	7.429%	$156.5993	$156.60	$156.60	$156.60
Purchase #3	$45.95	13.872%	$52.3242	$52.32	$52.30	$52.30
Purchase #4	$88.32	9.392%	$96.615	$96.62	$96.60	$96.60
Purchase #5	$6.86	11.511%	$7.6497	$7.65	$7.65	$7.60
Purchase #6	$11.78	11.743%	$13.1633	$13.16	$13.15	$13.20
Purchase #7	$92.41	10.477%	$102.0918	$102.09	$102.10	$102.10
7 purchase totals =	$522.62		$564.9162	$564.91	$564.85	$564.90