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	$19.79	7.643%	$21.3025	$21.30	$21.30	$21.30
Purchase #2	$74.26	12.445%	$83.5017	$83.50	$83.50	$83.50
Purchase #3	$131.67	8.277%	$142.5683	$142.57	$142.55	$142.60
Purchase #4	$249.95	9.730%	$274.2701	$274.27	$274.25	$274.30
Purchase #5	$232.61	3.426%	$240.5792	$240.58	$240.60	$240.60
Purchase #6	$178.69	11.335%	$198.9445	$198.94	$198.95	$198.90
Purchase #7	$73.59	9.785%	$80.7908	$80.79	$80.80	$80.80
7 purchase totals =	$960.56		$1,041.9571	$1,041.95	$1,041.95	$1,042.00