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	$9.78	13.160%	$11.067	$11.07	$11.05	$11.10
Purchase #2	$93.76	11.299%	$104.3539	$104.35	$104.35	$104.40
Purchase #3	$40.79	7.572%	$43.8786	$43.88	$43.90	$43.90
Purchase #4	$217.88	10.191%	$240.0842	$240.08	$240.10	$240.10
Purchase #5	$246.39	9.412%	$269.5802	$269.58	$269.60	$269.60
Purchase #6	$72.99	10.338%	$80.5357	$80.54	$80.55	$80.50
Purchase #7	$179.46	6.609%	$191.3205	$191.32	$191.30	$191.30
7 purchase totals =	$861.05		$940.8201	$940.82	$940.85	$940.90