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	$91.38	9.865%	$100.3946	$100.39	$100.40	$100.40
Purchase #2	$205.74	4.435%	$214.8646	$214.86	$214.85	$214.90
Purchase #3	$150.70	13.425%	$170.9315	$170.93	$170.95	$170.90
Purchase #4	$187.30	13.270%	$212.1547	$212.15	$212.15	$212.20
Purchase #5	$169.48	9.688%	$185.8992	$185.90	$185.90	$185.90
Purchase #6	$21.50	6.683%	$22.9368	$22.94	$22.95	$22.90
Purchase #7	$228.57	5.560%	$241.2785	$241.28	$241.30	$241.30
7 purchase totals =	$1,054.67		$1,148.4599	$1,148.45	$1,148.50	$1,148.50