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	$5.47	12.586%	$6.1585	$6.16	$6.15	$6.20
Purchase #2	$190.39	12.582%	$214.3449	$214.34	$214.35	$214.30
Purchase #3	$66.30	9.512%	$72.6065	$72.61	$72.60	$72.60
Purchase #4	$245.93	10.523%	$271.8092	$271.81	$271.80	$271.80
Purchase #5	$199.46	13.571%	$226.5287	$226.53	$226.55	$226.50
Purchase #6	$199.34	13.317%	$225.8861	$225.89	$225.90	$225.90
Purchase #7	$212.50	13.665%	$241.5381	$241.54	$241.55	$241.50
7 purchase totals =	$1,119.39		$1,258.8720	$1,258.88	$1,258.90	$1,258.80