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	$90.60	11.282%	$100.8215	$100.82	$100.80	$100.80
Purchase #2	$25.98	5.613%	$27.4383	$27.44	$27.45	$27.40
Purchase #3	$234.83	13.458%	$266.4334	$266.43	$266.45	$266.40
Purchase #4	$216.96	13.815%	$246.933	$246.93	$246.95	$246.90
Purchase #5	$247.94	12.232%	$278.268	$278.27	$278.25	$278.30
Purchase #6	$134.39	6.653%	$143.331	$143.33	$143.35	$143.30
Purchase #7	$145.55	12.822%	$164.2124	$164.21	$164.20	$164.20
7 purchase totals =	$1,096.25		$1,227.4376	$1,227.43	$1,227.45	$1,227.30