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	$239.59	4.598%	$250.6063	$250.61	$250.60	$250.60
Purchase #2	$247.57	5.354%	$260.8249	$260.82	$260.80	$260.80
Purchase #3	$233.83	9.874%	$256.9184	$256.92	$256.90	$256.90
Purchase #4	$136.60	10.794%	$151.3446	$151.34	$151.35	$151.30
Purchase #5	$28.34	12.581%	$31.9055	$31.91	$31.90	$31.90
Purchase #6	$115.58	9.342%	$126.3775	$126.38	$126.40	$126.40
Purchase #7	$5.98	6.854%	$6.3899	$6.39	$6.40	$6.40
7 purchase totals =	$1,007.49		$1,084.3671	$1,084.37	$1,084.35	$1,084.30