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	$142.54	8.184%	$154.2055	$154.21	$154.20	$154.20
Purchase #2	$60.26	12.191%	$67.6063	$67.61	$67.60	$67.60
Purchase #3	$112.88	7.820%	$121.7072	$121.71	$121.70	$121.70
Purchase #4	$63.63	12.240%	$71.4183	$71.42	$71.40	$71.40
Purchase #5	$80.30	6.127%	$85.22	$85.22	$85.20	$85.20
Purchase #6	$187.52	6.866%	$200.3951	$200.40	$200.40	$200.40
Purchase #7	$80.58	9.588%	$88.306	$88.31	$88.30	$88.30
7 purchase totals =	$727.71		$788.8584	$788.88	$788.80	$788.80