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	$52.54	13.432%	$59.5972	$59.60	$59.60	$59.60
Purchase #2	$55.60	6.250%	$59.075	$59.08	$59.10	$59.10
Purchase #3	$96.53	13.827%	$109.8772	$109.88	$109.90	$109.90
Purchase #4	$154.72	3.499%	$160.1337	$160.13	$160.15	$160.10
Purchase #5	$216.32	6.287%	$229.92	$229.92	$229.90	$229.90
Purchase #6	$177.25	7.449%	$190.4534	$190.45	$190.45	$190.50
Purchase #7	$13.83	12.189%	$15.5157	$15.52	$15.50	$15.50
7 purchase totals =	$766.79		$824.5722	$824.58	$824.60	$824.60