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	$20.38	11.710%	$22.7665	$22.77	$22.75	$22.80
Purchase #2	$186.45	8.520%	$202.3355	$202.34	$202.35	$202.30
Purchase #3	$112.30	3.801%	$116.5685	$116.57	$116.55	$116.60
Purchase #4	$17.50	5.633%	$18.4858	$18.49	$18.50	$18.50
Purchase #5	$83.58	7.443%	$89.8009	$89.80	$89.80	$89.80
Purchase #6	$121.63	7.379%	$130.6051	$130.61	$130.60	$130.60
Purchase #7	$36.55	6.488%	$38.9214	$38.92	$38.90	$38.90
7 purchase totals =	$578.39		$619.4837	$619.50	$619.45	$619.50