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	$40.90	6.715%	$43.6464	$43.65	$43.65	$43.60
Purchase #2	$156.82	4.699%	$164.189	$164.19	$164.20	$164.20
Purchase #3	$167.47	13.434%	$189.9679	$189.97	$189.95	$190.00
Purchase #4	$29.49	6.669%	$31.4567	$31.46	$31.45	$31.50
Purchase #5	$76.84	11.213%	$85.4561	$85.46	$85.45	$85.50
Purchase #6	$179.93	4.855%	$188.6656	$188.67	$188.65	$188.70
Purchase #7	$128.84	9.386%	$140.9329	$140.93	$140.95	$140.90
7 purchase totals =	$780.29		$844.3146	$844.33	$844.30	$844.40