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	$86.63	4.719%	$90.7181	$90.72	$90.70	$90.70
Purchase #2	$221.98	6.263%	$235.8826	$235.88	$235.90	$235.90
Purchase #3	$152.84	12.561%	$172.0382	$172.04	$172.05	$172.00
Purchase #4	$250.43	9.870%	$275.1474	$275.15	$275.15	$275.10
Purchase #5	$107.66	8.814%	$117.1492	$117.15	$117.15	$117.10
Purchase #6	$245.88	3.838%	$255.3169	$255.32	$255.30	$255.30
Purchase #7	$127.66	12.662%	$143.8243	$143.82	$143.80	$143.80
7 purchase totals =	$1,193.08		$1,290.0767	$1,290.08	$1,290.05	$1,289.90