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	$11.30	4.526%	$11.8114	$11.81	$11.80	$11.80
Purchase #2	$126.54	11.255%	$140.7821	$140.78	$140.80	$140.80
Purchase #3	$97.58	5.418%	$102.8669	$102.87	$102.85	$102.90
Purchase #4	$38.74	11.741%	$43.2885	$43.29	$43.30	$43.30
Purchase #5	$68.58	6.636%	$73.131	$73.13	$73.15	$73.10
Purchase #6	$148.56	11.647%	$165.8628	$165.86	$165.85	$165.90
Purchase #7	$97.33	4.352%	$101.5658	$101.57	$101.55	$101.60
7 purchase totals =	$588.63		$639.3085	$639.31	$639.30	$639.40