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	$240.38	12.277%	$269.8915	$269.89	$269.90	$269.90
Purchase #2	$205.27	6.493%	$218.5982	$218.60	$218.60	$218.60
Purchase #3	$29.27	3.392%	$30.2628	$30.26	$30.25	$30.30
Purchase #4	$213.92	12.873%	$241.4579	$241.46	$241.45	$241.50
Purchase #5	$103.94	7.154%	$111.3759	$111.38	$111.40	$111.40
Purchase #6	$147.26	6.871%	$157.3782	$157.38	$157.40	$157.40
Purchase #7	$102.67	7.607%	$110.4801	$110.48	$110.50	$110.50
7 purchase totals =	$1,042.71		$1,139.4446	$1,139.45	$1,139.50	$1,139.60