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	$11.77	13.172%	$13.3203	$13.32	$13.30	$13.30
Purchase #2	$250.71	5.741%	$265.1033	$265.10	$265.10	$265.10
Purchase #3	$178.25	10.245%	$196.5117	$196.51	$196.50	$196.50
Purchase #4	$208.57	12.665%	$234.9854	$234.99	$235.00	$235.00
Purchase #5	$62.77	3.771%	$65.1371	$65.14	$65.15	$65.10
Purchase #6	$198.94	12.868%	$224.5396	$224.54	$224.55	$224.50
Purchase #7	$85.34	5.690%	$90.1958	$90.20	$90.20	$90.20
7 purchase totals =	$996.35		$1,089.7932	$1,089.80	$1,089.80	$1,089.70