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	$199.77	11.868%	$223.4787	$223.48	$223.50	$223.50
Purchase #2	$173.28	13.317%	$196.3557	$196.36	$196.35	$196.40
Purchase #3	$225.86	13.479%	$256.3037	$256.30	$256.30	$256.30
Purchase #4	$31.81	13.217%	$36.0143	$36.01	$36.00	$36.00
Purchase #5	$27.52	10.271%	$30.3466	$30.35	$30.35	$30.30
Purchase #6	$54.61	9.329%	$59.7046	$59.70	$59.70	$59.70
Purchase #7	$103.99	12.729%	$117.2269	$117.23	$117.25	$117.20
7 purchase totals =	$816.84		$919.4305	$919.43	$919.45	$919.40