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	$39.34	10.617%	$43.5167	$43.52	$43.50	$43.50
Purchase #2	$128.40	8.497%	$139.3101	$139.31	$139.30	$139.30
Purchase #3	$232.46	11.774%	$259.8298	$259.83	$259.85	$259.80
Purchase #4	$145.71	10.513%	$161.0285	$161.03	$161.05	$161.00
Purchase #5	$90.47	11.731%	$101.083	$101.08	$101.10	$101.10
Purchase #6	$246.72	9.502%	$270.1633	$270.16	$270.15	$270.20
Purchase #7	$131.39	10.273%	$144.8877	$144.89	$144.90	$144.90
7 purchase totals =	$1,014.49		$1,119.8191	$1,119.82	$1,119.85	$1,119.80