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	$66.78	10.540%	$73.8186	$73.82	$73.80	$73.80
Purchase #2	$68.50	5.617%	$72.3476	$72.35	$72.35	$72.30
Purchase #3	$99.82	12.511%	$112.3085	$112.31	$112.30	$112.30
Purchase #4	$183.43	11.184%	$203.9448	$203.94	$203.95	$203.90
Purchase #5	$80.51	4.235%	$83.9196	$83.92	$83.90	$83.90
Purchase #6	$205.80	4.137%	$214.3139	$214.31	$214.30	$214.30
Purchase #7	$229.86	4.554%	$240.3278	$240.33	$240.35	$240.30
7 purchase totals =	$934.70		$1,000.9808	$1,000.98	$1,000.95	$1,000.80