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	$41.67	5.408%	$43.9235	$43.92	$43.90	$43.90
Purchase #2	$124.43	9.542%	$136.3031	$136.30	$136.30	$136.30
Purchase #3	$86.89	11.528%	$96.9067	$96.91	$96.90	$96.90
Purchase #4	$101.99	5.360%	$107.4567	$107.46	$107.45	$107.50
Purchase #5	$80.81	11.466%	$90.0757	$90.08	$90.10	$90.10
Purchase #6	$126.76	11.636%	$141.5098	$141.51	$141.50	$141.50
Purchase #7	$42.89	6.340%	$45.6092	$45.61	$45.60	$45.60
7 purchase totals =	$605.44		$661.7847	$661.79	$661.75	$661.80