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	$11.82	4.217%	$12.3184	$12.32	$12.30	$12.30
Purchase #2	$183.27	7.393%	$196.8192	$196.82	$196.80	$196.80
Purchase #3	$157.83	13.413%	$178.9997	$179.00	$179.00	$179.00
Purchase #4	$110.55	11.273%	$123.0123	$123.01	$123.00	$123.00
Purchase #5	$140.71	10.758%	$155.8476	$155.85	$155.85	$155.80
Purchase #6	$200.58	3.675%	$207.9513	$207.95	$207.95	$208.00
Purchase #7	$198.64	7.365%	$213.2698	$213.27	$213.25	$213.30
7 purchase totals =	$1,003.40		$1,088.2183	$1,088.22	$1,088.15	$1,088.20