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	$140.44	3.871%	$145.8764	$145.88	$145.90	$145.90
Purchase #2	$126.88	3.764%	$131.6558	$131.66	$131.65	$131.70
Purchase #3	$238.85	8.455%	$259.0448	$259.04	$259.05	$259.00
Purchase #4	$104.63	4.253%	$109.0799	$109.08	$109.10	$109.10
Purchase #5	$159.66	6.656%	$170.287	$170.29	$170.30	$170.30
Purchase #6	$81.58	7.746%	$87.8992	$87.90	$87.90	$87.90
Purchase #7	$161.26	13.190%	$182.5302	$182.53	$182.55	$182.50
7 purchase totals =	$1,013.30		$1,086.3733	$1,086.38	$1,086.45	$1,086.40