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	$11.39	4.459%	$11.8979	$11.90	$11.90	$11.90
Purchase #2	$24.73	12.398%	$27.796	$27.80	$27.80	$27.80
Purchase #3	$11.51	7.599%	$12.3846	$12.38	$12.40	$12.40
Purchase #4	$74.88	4.689%	$78.3911	$78.39	$78.40	$78.40
Purchase #5	$173.99	11.759%	$194.4495	$194.45	$194.45	$194.40
Purchase #6	$52.69	7.338%	$56.5564	$56.56	$56.55	$56.60
Purchase #7	$249.82	12.387%	$280.7652	$280.77	$280.75	$280.80
7 purchase totals =	$599.01		$662.2407	$662.25	$662.25	$662.30