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	$164.33	11.782%	$183.6914	$183.69	$183.70	$183.70
Purchase #2	$143.31	6.133%	$152.0992	$152.10	$152.10	$152.10
Purchase #3	$228.37	13.576%	$259.3735	$259.37	$259.35	$259.40
Purchase #4	$250.86	13.380%	$284.4251	$284.43	$284.45	$284.40
Purchase #5	$128.67	9.447%	$140.8255	$140.83	$140.85	$140.80
Purchase #6	$43.39	5.373%	$45.7213	$45.72	$45.70	$45.70
Purchase #7	$237.98	3.856%	$247.1565	$247.16	$247.15	$247.20
7 purchase totals =	$1,196.91		$1,313.2925	$1,313.30	$1,313.30	$1,313.30